Seasonic X-400 Fanless PSU

blog image

The Seasonic X-400 Fanless is based on the successful, 80 Plus Gold X-series platform introduced late last year. Company reps say the new fanless PSU was years in the making; ultimately, they had to await the development of a super-efficient platform. It was worth the wait.

Product
X-400 Fanless (SS-400FL)
computer power supply
Sample Supplier
Seasonic USA
Manufacturer
Seasonic Electronics
Suggested Price
US$139

The primary challenge for a fanless power supply in a computer is the elimination
of the heat generated by the conversion from AC to DC. The higher the conversion
efficiency, the simpler the task of cooling. The >90% efficiency of the 80
Plus
Gold rated Seasonic X-series power supplies is significantly higher
than any previous fanless PSUs, so the X-400 Fanless should come as no surprise.

The X-400 Fanless or SS-400FL is the first of two fanless models in the Seasonic
X-series power supplies. A 460W model is scheduled to hit the market in September.
The X-series is intended to span eight models, with the fanless units at the
bottom and 1000W and 1200W models at the top. As SPCR regulars are well aware,
a Seasonic X-650 reviewed in November 2009
garnered very high praise and earned our Editor’s Choice award. Aside from superb
electrical performance, the X-650 featured a successful "hybrid" cooling
system — hybrid meaning a cross between passive and active cooling. Its
fan simply stopped spinning at loads below ~200W in our hot test box, putting
the X-650 at the top of our quiet PSU roster. Interestingly, some of the newly
announced 80 Plus Gold Corsair AX series power supplies appear to be direct
family relations to the X-series.

Silent PC DIY enthusiasts, especially those building 24/7-on HTPCs, are an
obvious target market for the SS-400/460FL, but it isn’t that big a market.
So what are the other potential markets for fanless PSUs?

  • Specialist system integrators who build high end silent systems, especially
    home theater PCs where buyers tend to be well heeled and less price-conscious.
  • Specialist laboratory PCs that must not add to either noise or airflow in
    the test rooms.
  • Digital audio workstations for music production/recording work in studios.
  • PCs in medical applications where high reliability, low noise and no forced
    airflow are highly valued. (In a premium quality PSU, the fan is usually the
    least reliable part. PSU makers report that fan-related returns include regular
    though not numerous instances where the fan blades cut the fan’s own power
    leads.)

Seasonic has been an innovation leader in computer power supply design and
manufacturing for over 30 years, and a pioneer in high energy efficiency. Seasonic-made
PSUs have also dominated the top ranks of SPCR’s Recommended
PSU list
for years (under its own brand and under the brands of its
clients, such as Antec and Corsair). Back in October 2008, Seasonic
was the first to achieve the Gold 80 Plus award for ATX12V PSUs
, specifically
for its 550LT, 650 KM and 750KM models, all using the technology featured in
the X-series.

Our X-400 Fanless sample is from the first production batch, the bulk of which
should be at retailers warehouses by mid August. Along with the X-400 sample,
Seasonic included a reviewer’s guide, photos and other technical documentation
on a USB flash drive.

PACKAGING & FEATURES


The gold-black retail box is similar to others of the X-series. The
little box contains the USB flash drive of data and information for
reviewers


The packaging and presentation inside is first class, with all the cables
in a pouch, and the PSU in a velvet drawstring bag.


Also included are plastic ties and velctro straps for cable management.
As with other X-series models, every cable is detachable.

Seasonic X-400 FEATURE HIGHLIGHTS (from the
web product
page
)
FEATURE & BRIEF Our comment
Core Features
80PLUS Gold Certified Super High Efficiency Assured 90% power conversion efficiency.
DC to DC Converter Design; Patented
DC Connector Module with Integrated VRM
[Voltage Regulator Module]
DC-to-DC conversion for the lower voltage
lines is not unusual, but Seasonic’s implementation is unique.
Fanless – 0dBA If electronic noise (coil whine) is
kept under control, the unit should be silent.
"Green Innovation" Features for Extended Product
Life, High Quality, High Efficiency, and Competitive pricing
Highly Reliable 105°C Japanese Capacitors

Many high end PSUs flaunt this feature, including Seasonic’s others.

Conductive Polymer Aluminum
Solid Capacitors
These advanced caps are also
used on motherboards.
Super High Efficiency [up to 90%]
Green solution for lowering energy consumption, noise & heat.
OK.
Dual Sided PCB Layout
Better utilization of PCB space to enhance quality and performance.
OK.
Tight Voltage Regulation [±3%] More stringent than the ±5% recommended
by the Intel ATX12V PSU design guide.
Ample +12V Output 33A (396W) on a single rail.
Safety: UL/CUL, TUV,
CE, CB, CCC, FCC Class B, C-Tick, GOST-R, UkrTEST, BSMI, Semko
Very good.
Protection from short
circuits (SCP), over voltages (OVP), over power (OPP), over temperature
(OTP), and over current (OCP)
The more the merrier. OTP
is particular important for a fanless PSU.
Universal Input, Active PFC Like just about every PSU
on the retail market… but Seasonic was
the pioneer with these features
on computer PSUs.
MTBF: Over 150,000 hours
at 25 Deg C.
Very good.
Seasonic 5 year warranty Excellent!
Net Weight: 3 lbs 10 oz
(w/o cables)
Size: W150 x L160 x H86 mm
Quite light for a fanless
PSU.
Seasonic SS-400NF Specifications
AC Input
90~264VAC 6~3A 50/60 Hz
DC Output
3.3V
5V
12V
-12V
5Vsb
20A
20A
33A
0.5A
2.5A
100W
396W
6W
12.5W
400W
Line regulation (all DC rails) ±1%
Load regulation (all DC rails) ±3%
Operating Temp: 0~50°C, 100% Continuous Power @ 50°C

VISUAL TOUR

The first glance when the PSU is removed from its soft pouch shows two distinct
things:

  1. The casing is completely vented, with hex holes on top that are bigger than
    the ones used for the back panel exhaust. It’s basically an expansion of the
    intake fan grill used on fan-equipped Seasonics.
  2. A big notice tells to "install with the ventilation top cover facing
    UP". This is the side where the 120mm fan is mounted on the higher power
    X-series models; it’s normal for the PCB to be on the top side of the PSU,
    with components hanging down from it. So Seasonic means for the X-400 to be
    mounted turned over, 180° from the norm. Note that there are enough tapped
    mounting screw holes so that the PSU can be mounted either way, so if you
    disagree with Seasonic’s advice for your PC setup (and there are so many different
    types of cases that use ATX PSUs these days), you can try it the other way
    without any hacking.

This worthy of further discussion, later.

One other observation is that the X-400 is a complete departure from the norm
in that it’s a lightweight, only a little over 3.5 lbs without cables. This
is in stark contrast to every other fanless ATX PSU reviewed in the past eight
years — they have been very heavy, easily 5~6 lbs on average, with massive
amounts of extruded aluminum, some of which is used for the casing.


The side which holds the fan in higher power X models has the same
basic grill, expanded across most of its area, and a notice calling
for the unit to be installed that side up.


The modular cables are nicely finished.

Output Cables

1 – ATX connector 20+4 pin (600mm)
1 – CPU connector 4/8-pin (600mm)
1 – PCIe 6/8-pin (600mm)
1 – three SATA connectors (750mm)
1 – two SATA connectors (480mm)
1 – three 4-pin peripheral connectors (750mm)
1 – two 4-pin peripheral connectors (480mm)
1 – two floppy drive connectors on Y adapter (150mm)

Like other X-series models, the X-400 casing is a departure from
the normal dual C-shaped clamshell. The metal is thicker and is fitted together
tightly with great precision — though Seasonics have always been excellent
in this regard. The black and gold color scheme continues in the paint job and
labels. The X-400 Fanless exudes quality in every way.


It’s well ventilated on almost every side…
…even the normally unvented "bottom". The same smart-keyed
output connector scheme is used as in the X-650, but fewer of them, reflecting
the X-400’s lower output rating.


The label is in several languages and boasts a myriad of safety approvals.

INSIDE

The the top vented panel came off with the removal of four screws. Compared
to the X-650, th heatsinks are larger… but puny compared to the massive aluminum
extrusions used in fanless 400W power supplies that we’ve examined in the past.
As usual, the interior is extremely tidy and meticulously laid out.

Click for large image
The X-400 heatsinks have wide spaced fins, and they are bigger than
those in the X-650, but not that much bigger…
(Click on image for larger image in new window)


…as you can see in this photo from our X-650 review.

Click for large image
Another view of the X-400 Fanless.
(Click on image for larger image in new window)

This photo helps to clarify some of the changes in the X-400 Fanless…


…compared to a photo of the X-650 from a similar angle.

The metal plate on the patent-pending DC/DC Connector Module (12VDC
to 5VDC and 3.3VDC) is the only extra heatsink the X-400 has gained compared
to the X-650. Every other heatsink in the X-400 is matched by one in the X-650.

Seasonic’s explanation of the DC/DC Connector Module in the X-series
design is worth repeating. By making the conversion from 12VDC to 5VDC and 3.3VDC
on this module, the losses inherent in low voltage electricity transfer are
minimized.

TESTING

For a fuller understanding of ATX power supplies, please read
the reference article Power
Supply Fundamentals
. Those who seek source materials
can find Intel’s various PSU design guides at Form
Factors
.

For a complete rundown of standard testing equipment and procedures,
please refer to SPCR’s PSU
Test Platform V4.1
. The testing system is a close simulation of a moderate
airflow mid-tower PC optimized for low noise.

Acoustic measurements are now performed in our anechoic chamber with ambient level of 11 dBA or lower, with a PC-based spectrum analyzer comprised of SpectraPLUS software with ACO Pacific microphone and M-Audio digital audio interfaces.

In the test rig, the ambient temperature of the PSU varies proportionately
with its output load, which is exactly the way it is in a real PC environment.
But there is the added benefit of a high power load tester which allows incremental
load testing all the way to full power for any non-industrial PC power supply.
Both fan noise and voltage are measured at various standard loads. It is, in
general, a very demanding test, as the operating ambient temperature of the
PSU often reaches >40°C at full power. This is impossible to achieve
with an open test bench setup.

SPECIAL TEST SETUP FOR X-400 FANLESS

Normally, a 120mm fan is responsible for "case airflow" of our PSU test hotbox, and run at a steady slow speed (~800 RPM, ~13 dBA@1m)
at low loads. With the X-400 Fanless, we chose to run the tests without
any exhaust fan
, the point of the exercise being to determine whether
the X-400 can keep running in ridiculously hot conditions when pressed really
hard. This test with no exhaust fan in the hotbox would represent the most extreme
thermal conditions in a poorly designed fanless DIY system… which probably
happens more than most fanless PSU sellers would like.


No exhaust fan for testing the X-400.

The Seasonic’s vented-side-up installation gives it a big advantage
in our test rig: Since there is no top cover over the PSU, the heat from the
X-400 can vent freely into the room by convection. But keep in mind that this
advantage also holds for all other PSUs we’ve tested in the past, including
the fanless ones. You could say that the heat in the hotbox is excessively high,
higher than in any real PC… and this is somewhat offset by the open top over
the PSU.

If an exhaust fan was used, the vents in the X-400 would act as
intake vents for the fan, which would draw air from the outside through the
PSU. This is the air flow pattern we’ve see with other openly vented fanless
PSUs like the FSP Zen; the closest vents in the case with the least impedance
become intakes for the back panel exhaust fan.


The PSU load tester was not run fanless. There is no way 400W can be dissipated
safely in our load tester without some forced airflow. This is provided
by four slow-spinning 80mm fans that exhuast the heat from the DBS-2100
load test device into our hotbox, whose resistor banks take about half
the load at 400W. The only escape paths for the hot air is through the
PSU and the "back panel" vent where the exhuast fan usually
goes.

TEST RESULTS

The ambient temperature was 23~24°, and the ambient noise
level was 14~15 dBA. The PSU was allowed to run at each power level for about
20 minutes before any measurements were taken.

OUTPUT, REGULATION & EFFICIENCY: Seasonic
X-400 Fanless

DC Output Voltage (V) + Current (A)

DC Output

AC Input

Calculated Efficiency
+12V
+5V
+3.3V
-12V
+5Vsb
12.20
0.97
5.03
0.97
3.38
0.96
0.1
0.1
21.6
31
69.8%
12.20
2.69
5.03
0.97
3.38
0.96
0.1
0.1
42.6
53
80.4%
12.17
3.60
5.02
1.91
3.37
2.71
0.2
0.2
65.9
78
84.5%
12.17
5.27
5.00
2.77
3.36
2.56
0.2
0.3
90.5
106
85.4%
12.14
8.67
5.00
5.40
3.35
3.52
0.3
0.5
150.1
169
88.8%
12.10
12.13
5.00
5.37
3.33
5.21
0.4
0.5
198.2
215
92.2%
12.05
15.50
4.98
6.10
3.33
4.98
0.6
1.5
248.4
273
91.0%
12.05
18.50
4.97
7.10
3.31
6.97
0.7
2.0
299.8
330
90.9%
12.04
25.86
4.97
8.68
3.30
6.97
0.8
2.5
399.3
444
89.9%
Crossload Test
12.08
32.77
5.00
2.77
3.37
2.71
0.5
1.5
301.4
327
92.2%
+12V Ripple (peak-to-peak): <13mV @ <150W
~ 18mV @ 400W
+5V Ripple (peak-to-peak): <5mV @ <150W ~ 7mV @ 400W
+3.3V Ripple (peak-to-peak): 5mV @ <150W ~ 12mV @ 400W
NOTE: The current and voltage for -12V and
+5VSB lines is not measured but based on switch settings. It is a tiny
portion of the total, and errors arising from inaccuracies on these
lines is <1W. Three separate 12V loads were used, but as the X-400
has just one 12V line, all the 12V current was summed for simplicity.
OTHER DATA SUMMARY: Seasonic X-400 Fanless
DC Load (W)
22
43
66
90
150
198
248
300
399
Intake °C
24
25
27
31
35
37
37
39
43
"Exhaust" °C
28
30
31
36
39
39
40
43
54
Temp Rise °C
4
5
4
5
4
2
3
4
11
SPL (dBA@1m)
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
Power Factor
0.89
0.97
0.98
0.99
0.99
1.00
1.00
1.00
1.00

AC Power in Standby: 0.3W / 0.1 PF
AC Power with No Load, PSU power On: 7.2W / 0.70 PF
NOTE: The ambient room temperature during
testing can vary a few degrees from review to review. Please take this
into account when comparing our PSU test data.

1. EFFICIENCY This is a measure of AC-to-DC
conversion efficiency. The ATX12V Power Supply Design Guide recommends 80% efficiency
or better at all output power loads. 80% efficiency means that to deliver 80W
DC output, a PSU draws 100W AC input, and 20W is lost as heat within the PSU.
Higher efficiency is preferred for reduced energy consumption and cooler operation.
It allows reduced cooling airflow, which translates to lower noise. The 80 Plus
Gold standard requires 90% efficiency at 50% of rated load, and 87% efficiency
at both 20% load and full rated load.

Keep in mind that the testing for 80 Plus approval is done at
normal ambient room temperature. The 80
Plus Testing Guidelines (PDF)
specify only that "ambient temperature
shall be maintained at 23°C ± 5°C throughout the test
."
In contrast, the ambient temperature of the SPCR test system is directly proportionate
to the load. At low load, the air intake is at or just above room temperature,
but as load is increased, the temperature rises steadily. This is an extremely
tough test condition, as PSU efficiency naturally drops off at high and low
loads; combine high load with high temperature and it’s essentially a PSU torture
chamber.

At the super low 20W load, efficiency was excellent at 69.8%,
compared to 65% in the X-650. Efficiency rose quickly as the load was increased.
80% efficiency was reached around the 40W mark, but our sample did not quite
reach 87% at 80W (as called for in the 80 Plus Gold requirement). It probably
consumed 1-2W more than required, as 86% efficiency was seen at 90W load. (A
Chroma PSU test report Seasonic ran on this very sample and sent along as part
of the reviewer package showed 87.84% efficiency at 80W load. We’re inclined
to trust their Chroma report more than our own test result; there are undoubtedly
a few points of departure from "true" values on our homebrew rig.)
By 150W, efficiency reached nearly 90%. At 200W, >92% efficiency was reached.
With higher load, and higher operational temperature in the SPCR test box, efficiency
dropped a bit, but still remained just about at 90% even at full power, at over
40°C temperature in the hotbox.

These are great results, as expected. We’ve never seen such high
efficiency at such low loads, and the efficiency curve is extremely flat, despite
the absence of active cooling for the PSU. The 90% efficiency at full load was
a real surprise, as we expected it to sag much lower in the hot conditions.

2. VOLTAGE REGULATION refers to how stable the output voltages
are under various load conditions. The ATX12V Power Supply Design Guide calls
for the +12, +5V and +3.3V lines to be maintained within ±5%.

At all load levels, the critical 12V line was within 0.2V (~1.7%)
of 12V, and even at the highest loads, it never dropped below 12V. This is excellent
performance. The 3.3V regulation was within 0.08V, while the 5V line was off
by 0.06V (2%) at worst. The sample exceeded Seasonic’s own stringent 3% spec
for voltage regulation.

3. AC RIPPLE refers to unwanted "noise"
artifacts in the DC output of a switching power supply. It’s usually very high
in frequency (in the order of 100s of kHz). The peak-to-peak value is measured.
The ATX12V Guide allows up to 120mV (peak-to-peak) of AC ripple on the +12V
line and 50mV on the +5V and +3.3V lines. Ripple on all the lines was absurdly
low at all power levels. Even at maximum power, the 12V ripple stayed under
20mV. Along with the Seasonic X-650, it is the best ripple we’ve measured.

4. POWER FACTOR is ideal when it measures 1.0. In the most
practical sense, PF is a measure of how "difficult" it is for the
electric utility to deliver the AC power into your power supply. High PF reduces
the AC current draw, which reduces stress on the electric wiring in your home
(and elsewhere up the line). It also means you can do with a smaller, cheaper
UPS backup; they are priced according to their VA (volt-ampere) rating. Power
factor was near perfect throughout the test range.

5. LOW LOAD TESTING revealed no problems starting at very
low loads. Our sample had no issue starting up with no load, either, and the power draw was much lower than normal.

6. LOW & 240 VAC PERFORMANCE

The power supply was set to 300W load with 120VAC through a hefty
variac in the lab. The variac was then dialed 10V lower every 5 minutes. This
is to check the stability of the PSU under brownout conditions where the AC
line voltage drops from the 110~120V norm. Most full-range input power supplies
achieve higher efficiency with higher AC input voltage. SPCR’s lab is equipped
with a 240VAC line, which was used to check power supply efficiency for the
benefit of those who live in 240VAC mains regions.

Various VAC Inputs: X-400 @ 300W Output
VAC
AC Power
Efficiency
245V
321W
93.5%
120V
330W
90.9%
100V
340W
88.3%

Efficiency improved around 2.4% with 244VAC input at this load.
The sample passed the 100VAC minimum input without any issues. Neither voltage
regulation nor ripple changed appreciably during the test.

7. TEMPERATURE & COOLING

As mentioned earlier, the flipped over recommended position of
the X-400 Fanless gave it a distinct advantage in our PSU test hotbox. Nevertheless,
it’s impressive how cool the unit really ran. Note that the "exhaust"
temperature isn’t really that; the thermal sensor was simply stuck on the middle
of the back panel. Periodic spot checks with an infrared non-contact thermometer
showed temperatures of 65~70°C around the heatsinks and the main capacitor during
the 20~30 minutes of operation at full 400W load, which caused no distress whatsoever.

8. ACOUSTICS

Normally. this is the end of our electrical and thermal performance
analysis, and we move on to acoustics. However, there’s simply no acoustics
to be discussed. There are also no recordings of the PSU’s noise. The X-400
Fanless remained silent from no load all the way to full 400 load throughout
the testing period. This is not to say the silence was absolutely complete;
from 6" away, at some load combinations a faint buzz could be heard. But
for all practical purposes, the X-400 is indeed silent. We said this about the
Silverstone ST45NF; this Seasonic is at least as quiet.

9. LONG TERM, FULL POWER, THERMAL TORTURE TEST

This is a test we have never run on any PSU before: Long-term,
full load test without an exhaust fan in our PSU hotbox. It was mentioned earlier
that even running this box without the exhaust fan is not normal. Commercially
manufactured PSU load testers have non-defeatable, multiple high speed fans
to keep themselves cool. This is a major reason why we use our custom-cobbled
load tester: It lets us turn the fans off entirely when measuring or recording
PSU noise. So why run this test on the X-400 Fanless? Well, almost on a dare.

In direct discussions about the X-400 Fanless, Seasonic reps were
brimming with confidence that their new baby could not only perform just like
a fan-cooled 400-watter, but even deliver full power under extremely low airflow
conditions, such as one might find in a fanless (or single fan) silent PC. The
parts in the X-400 FL are apparently robust enough that if it was fan cooled,
it could easily be rated for 700W. This led to our running the normal tests
without an exhaust fan. When our Seasonic rep found out the 30 minute duration
of the 400W test load, he wanted us to try running it at full power for 24 hours,
as is often done for testing of mission-critical server PSUs — which are
never fanless.

The challenge was on. So, the X-400 Fanless was set to full load
without any exhaust fan in the test hotbox, and left to run as long as possible.
It was decided early on that 24 hours continuous was not going to be practical.
For safety reasons, the test would be monitored regularly (about once every
half hour) by a physically present person. That’s your author. The test was
begun at about 8 AM with 22~23°C ambient room temperature, and left to run until
11 PM that night, a total of 15 hours. The ambient temperature in the room climbed
to 26~27°C by 1 PM, stayed around there for several hours, and only declined
down to 24°C at 11 PM.

The temperature in the hotbox directly beneath the PSU ranged
56~60°C. Spot checks with the aforementioned infrared thermometer showed temperatures
inside the X-400 as high as 82~84°C; mostly it hovered close to but under 80°C.
The efficiency dropped as the PSU heated up. The 444W AC input seen after half
an hour rose gradually about 10~12W higher during the hottest part of the day.

The end result after 15 hours: The X-400 Fanless survived the
test. Furthermore, it worked perfectly the next day — and ran another 12
hours at the same load and conditions. At the end of the second day, a 1500W
hair dryer was brought into play while the PSU was at full load, blowing the
hot air down into the open grill cover of the X-400 to see what would happen
with thermal overload. In a minute, the PSU shut down with a little click, the
Over Temperature Protection finally kicking in. The IR thermometer showed temperatures
of over 90°C around the main heatsinks. The AC cord was unplugged, the power
switched off for a few minutes, then it was turned back on — with no change
to the load settings: The X-400 powered back up without a hitch and kept running.
The hair dryer was used several times to force OTP, just to check on the protection
function. It worked without a flaw about half a dozen times. The X-400 sample
is now powering a new system being set up for use in the lab.

It’s hard to imagine any other fanless PSU surviving our long
term full power torture test… but it was a valid question that came up, a
question that we decided to answer in Fanless
PSU Torture Test Roundup
.

10. IN A REAL SYSTEM?

How would the X-400 handle the heat in a real computer case where the
top would not be so wide open to the outside air? The answer is that it will
probably do fine in most systems (and modern cases) that are reasonably thought
out for cooling, even with minimal airflow. Consider the following points:

  • The way most people and programs use real computer systems results in dynamic
    — constantly changing, that is — power demand. Most computers run
    pretty close to idle much of the time, with short peaks into high power. Even
    modern 3D gaming doesn’t redline the PC constantly, there is always some up/down
    in power. In other words, our torture test of the X-400 Fanless is an unrealistically
    extreme, worst case scenario.
  • One of the advantages in a real computer is cooling by conduction from the
    casing of the PSU to the metal case to which it is tightly bolted. This conduction
    cooling is missing in our test hotbox.
  • Since HTPC system are probably the first target market, consider that many
    of the best HTPC cases we’ve reviewed have excellent airflow and open venting
    in, around or near the PSU. Think of Antec Fusion, Fusion Max, Silverstone
    GD05/06, for example — all place the PSU with space over it and vent
    holes or grills to the outside.
  • Then there are the many mid-tower and larger cases that put the PSU at the
    bottom, either with venting above or below, where you can experiment with
    flipping the X-400 one way or the other. The X-400 would fare well in such
    cases. Think Antec P180 series, Antec 3480 (with open vent above PSU), Antec
    gaming cases, Fractal R2, Silverstone Raven and Fortress models, Coolermaster’s
    CM690, CM Storm, HAF series, and a dozen Lian Li models with bottom PSU placements.
    In fact, the bottom mounted PSU is almost the rule among quality performance
    cases these days.

COMPARISONS

The comparison table below shows the SPL versus Power Load data on all the
PSUs tested in the anechoic chamber thus far. No comment is really needed.

Comparison: Various PSUs Noise (dBA@1m) Vs. Output
in Anechoic Chamber
Model
90W
150W
200W
250W
300W
400W
500W
6-700W
850W

Seasonic X-400
<10 (immeasurable)
n/a
n/a
n/a

Enermax Modu/Pro87+ 500
11
11
11
11
14
20
23
n/a
n/a

Seasonic X-650
<10
11
12
14
16
31
31
32
n/a

Nexus Value 430
11
11
16
18
18
19
n/a
n/a
n/a
Antec CP-850
12
12
12
14
14
26
40
44
45

Seasonic M12D 850W
14
14
14
14
14
24
37
42
42

Enermax Modu82+ 625*
13
13
14
15
16
26
36
37
n/a
Coolermaster M700W
14
14
18
21
25
27
34
34
n/a
Chill Innovation CP-700M
15
15
15
15
17
30
34
34
n/a
Antec Signature 650
15
15
15
18
18
28
36
47
n/a
SilverStone DA700
18
18
18
18
23
32
35
41
n/a
Nexus RX-8500
14
14
17
22
28
32
32
33
33
NesteQ ECS7001
22
22
22
21
23
25
36
37
n/a
PCPC Silencer 610
20
24
24
24
24
30
40
50
n/a
The green boxes represent >30 dBA@1m SPL.
*Guesstimates based on the Modu82+ 425’s idle in the chamber and the Modu82+
625’s load test.

Caution: Please keep in mind that
the data in the above table is specific to the conditions of our test setup.
Change the cooling configuration, the ambient temperature and any number of
other factors, and you could change the point at which the fans start speeding
up, as well as the rate of the rise in speed. The baseline SPL is accurate,
however, probably to within 1 dBA.

CONCLUSIONS

Expectations ran high for the X-series 80 Plus Gold Seasonic power
supplies, but our first reaction to the X-400 Fanless was admittedly less than
enthusiastic. With the X-series already fanless to ~200W load and extremely
quiet even after the fan starts spinning, why bother with a fanless one with
all the potential headaches? It’s a pleasant surprise — nay, a shock! —
to find we were very wrong. The X-400 Fanless is the most impressive fanless
PSU we’ve had the pleasure to examine, and we’ve examined just about all of
them over the years. Electrical performance is stellar, the build extremely
sturdy and well-executed, the all-detachable cables delightfully user-friendly,
and finally, the sheer toughness of the product under extreme heat over long
hours of excessive load is head, shoulders and entire torso above most of the
other fanless units. Many a fan-cooled PSU would not survive our torture test.

The robustness of this power supply makes it possible to use it
in systems with components that could demand the full rated 400W, unlike other
fanless PSUs. In the past, users (including us) quickly learned to baby their
fanless PSUs and keep them running cool in minimalist systems that drew very
little power, perhaps no more than 30-40% of the PSU’s rated power. Otherwise
overheating and shortened component life could be expected. With the X-400 Fanless,
these users will have to unlearn their past lessons, as the X-400 can pump out
full power even under extremely hot conditions. This is not to say that thermal
issues can be ignored; it’s always up to the system builder to ensure adequate
cooling and ventilation for components.

Another noteworthy point is that the X-400 Fanless happens to
be the only sub-500W ATX12V power supply on the retail market that is 80 Plus
Gold certified. That it is also fanless is pretty amazing. Yes, there are some
lower power OEM 80 Plus Gold units employed by Dell and other big PC makers,
but they’re extremely customized for their application with short cables, etc,
and not for retail sale. Every other retail-packaged Gold rated PSU is higher
power, typically 500W and up. The main reason for the scarcity of lower power
Gold models is due to user perceived need for higher power PSUs (a need encouraged,
of course, by the PSU vendors) which makes lower power models harder to sell.
There is a technical challenge, the difficulty of achieving high efficiency
at very low load: 20% of 400W is only 80W. We’ve long noted how PSU efficiency
drops dramatically at lower loads (and also at higher loads, but less so.)

With the solidly performing Silverstone ST45/40NF and perhaps
the cheaper 400W FSP Zen, we had felt the fanless PSU market well served. There
couldn’t be much demand, anyway. But the Seasonc X-400 Fanless (and the soon-to-come
X-460 Fanless) might be compelling enough to create a resurgence in fanless
PSUs, not only among DIY silent fanatics but more mainstream builders and commercial
system integrators as well. Backed by Seasonic’s generous 5-year warranty, and
their long history of solid customer support on high quality products, the X-400
could be the start of something like a silent fiefdom in the world of computer
power supplies.

The Seasonic X-400 Fanless is a superb power supply. It’s more
than just an X-series PSU without a fan. It stands on its own as a product carefully
engineered to serve its function, and it deserves our highest recommendation.

Seasonic X-400 Fanless Balance Sheet
Likes

* >90% efficiency in typical use
* Silent
* Extremely hardy in hot conditions
* Electrical performance is tops
* Hardly any buzz even close up
* Clever, innovative engineering
* Great quality components
& build
* All modular cables
* 5-year warranty

Quibbles

* Price? (About the only thing we could quibble about… but then all fanless
PSUs are pricey; finally, this is one that seems well worth the money.)

Much thanks to Seasonic USA for this review sample.


Seasonic X-400 Fanless: SPCR Editor’s Choice Award

* * *

SPCR Articles of Related Interest:
Power Supply Fundamentals

Recommended Power Supplies
SPCR PSU Test Rig V.4.1
X-650: Seasonic hits Gold
Enermax Modu87+ 500W 80 Plus Gold
Silverstone Nightjar ST45NF:
450W Fanless

Silentmaxx
Fanless 400W MX460-PFL01 PSU (FSP Zen)

* * *

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