Seasonic S12-500 & S12-600 Power Supplies

Table of Contents

They are the most powerful of the S12 series, and they are based on a more efficient circuit design than the smaller models in the line. The S12-430 is the current quiet leader among fan-cooled PSUs, but the 500 and 600 have even higher efficiency and dual PCI-e vidcard support for SLI. And they all have new Adda brand 120mm fans. SPCR’s full review on the S12-500 and S12-600.

May 22, 2005 by Mike
with Devon Cooke

*POSTSCRIPT added Oct. 22, 2005*

Seasonic S12-500 ATX Power Supply
Model SS-500HT Active PFC F3
Seasonic S12-600 ATX Power Supply
Model SS-600HT Active PFC F3
S12-500: US$130
S12-600: US$160

Seasonic is one of the longest-established makers of computer power supplies, and their products have consistently won respect from SPCR. The S12-430 we reviewed around two months ago turned out to be the one of most efficient fan-cooled PSU encountered, and also the quietest by a pretty big margin. Early production samples of the highest powered models in the S12 line, the 500 and 600, were also on hand at the time of the review, but Seasonic requested that we delay the review until newer samples were made available. A production change in the fan was coming, and this would affect the entire S12 line.

The Seasonic S12-500 and S12-600 differ from the lower powered S12 models more than just by power rating. These models actually use a different circuit design than the lower power models. Their model number, SS-500/600HT Active PFC F3, is different from the rest of the S12 line, SS-330/380/430HB Active PFC F3. The latter models feature upgraded variants of the circuit design used in the now-discontinued Super Tornado, while the 500 and 600 are entirely new. There is a third model, SS-400HT Active PFC F3, that logically belongs with the S12-500 and S12-600, but for whatever reasons, it appears to be unavailable for the retail market at this time.


The SS-xxxHT Active PFC F3 models have all been 80 PLUS certified.
Regular readers of SPCR (and dedicated observers of the power supply scene) will know about 80 PLUS. SPCR provided news coverage about this initiative to promote the use of efficient power supplies in computers. There was also related discussion on page three of the article, A New Energy Star.

80 PLUS is described as “a national buy-down program for desktop computers and desktop-derived servers that contain highly efficient power supplies.” The program invites submissions of PSUs, which are tested, and if the units pass, they become 80 PLUS approved. The test is quite tough: It calls for 80% or better efficiency at 20%, 50% and 100% of a PSU’s rated power output. When a system integrator uses any 80 PLUS certified PSUs in systems, they can receive rebates through the 80 PLUS program, ostensibly to offset the initial higher cost of these highly efficient PSUs. You can check out all the details of the program, administered by Ecos Consulting, a company that “only undertakes projects that make a positive environmental impact”, at the 80 PLUS web site.

The Seasonic SS-400HT APFC F3 was the first PSU to be approved by the 80 PLUS program. There are now four Seasonic PSU models on the approved products list. At time of posting, three other brands each feature a model on the an 80 PLUS approved PSU list.

What all this means to the end user is that the S12-500 and S12-600 should be >80% efficient at all power loads above 100W and 125W respectively. In SPCR’s test rig, the S12-430 achieved the requisite >80% efficiency between 90W and 250W load but fell shy of it at maximum load. The 500 and 600 shouild fare better.


August 3, 2005

It came to our attention recently that the S12-500 and S12-600 are NOT 80 Plus approved, as thought previously. Seasonic’s 80 Plus approved models are special OEM variants of the SS-400HT, SS-500HT and SS-600HT. The S12-500 / 600 have the same basic design, mechanically and electronically, but with longer output cables and the black paint finish, along with the box, manual and other accessories. The S12-500 and S12-600 are best viewed as variants of the SS-xxxHT OEM line. The 80 Plus approved SS-400HT, SS-500HT and SS-600HT models are OEM variants that come with special 80 Plus label.

This does not change the rest of the contents of our review nor our opinion of the S12-500/600.


The retail boxes for the 500 and 600 have new sticker labels that suggest changes and improvements.

New stickers on the box.

The blue orca image is now flanked by two prominent labels on the top left corner:

Two new labels on the S12-500 and S12-600 box.

It turns out that the top larger sticker applies to all of the S12 line:

120mm Double Ball Bearing Fan – It’s not clear exactly what type of ball bearing was used in the previous Yate Loon model fans that came in these S12s, but it must have been different for this point to be made. Seasonic states that the change was made in order to reduce rejects on the production line and to improve consistency.

Long-lived Aluminum Electrolytic Capacitor – Apparently, higher quality Japanese aluminum electrolytic capacitors are used for greater reliability and stable performance. More common China-made capacitors must have been used before, as is typical of most PSUs. There have been incidents of motherboard and PSU brands being affected by leaking capcitors sourced from China starting from ~2 years ago.

The second smaller sticker applies only to the S12-500/600:

Support SLI – PCI-Express X2 – Two 6-pin connectors with sufficient current capacity for PCI-E & SLI systems are provided. This is to ensure gamers get all the bang they need. Only the 500 and 600 are so equipped because they’re the models deemed to be high enough power capacity to handle SLI.

A news release detailing these improvements can be found at Seasonic’s web site.

The PSUs themselves do not appear much different than the early samples or the S12-430 except for the dual 6-pin PCIe connectors and a few subtleties. The contents of the box are also the same.

Clockwise, from top left: S12-600, box, Dr. Cable kit, instruction
booklet, mounting screws, Seasonic sticker, 4-pin Molex to 3 fan headers adapter,
AC cable.

There are a few vents on two other sides

Here’s where some differences show up: The S12-600 (and
500) on the left has smaller and fewer vents all around compared to the
S12-430 on the right, and the output cables are positioned so that they
exit on the side closest to the motherboard when installed in a typical
ATX case. Most users would say this cable positioning is better for cable

For the record, here’s the label from the S12-500. The one on the 600 is
identical except for the particulars.

Feature Highlights of the Seasonic S12-430
Complies with Intel ATX12V v2.0
Supports the latest
motherboards and processors.
S2FC Smart & Silent Fan Control
If it is unchanged from the Rev. A3 Super Tornado, it is about the best fan controller we’ve seen in a PSU. We’ll see.
Active PFC environment friendly technology
Almost every Seasonic we’ve looked at has had it for three years; now more common.
Universal Free Input:
As in previous Super series, can be useful.
Long-lived Aluminum Electrolytic Capacitor Not in first batches of the S12; this is part of the new & improved S12. If it means better reliablity, then great.
Forward Converter: Advanced design
Instead of a half-bridge rectifier, apparently.
Dual 12V
for CPU and peripherals
Specified by ATX12V v2.0
20+4 Pin Main Connector: Switches back and forth easily from 20 pin to 24 pin. One less bit of cable clutter, and reduced contact resistance as a 24-to-20 pin adapter is not used.
Short circuit, over voltage & over power protection Very nice.
Supports SLI / PCI Express
Dual PCIe 6-pin for high power VGA. Earlier versions had just one.
Supports Dual CPU motherboard 8-pin 12V cable
Safety / EMI Approvals: CE / TUV EN60950 / UL60950 / CSA / FCC / NEMKO Generally,
the more the better.
SPECIFICATIONS: Seasonic S12-500
AC Input
100-240V ~7A 50/60 Hz
DC Output
Maximum Output Current
Maximum Combined
SPECIFICATIONS: Seasonic S12-600
AC Input
100-240V ~7A 50/60 Hz
DC Output
Maximum Output Current
Maximum Combined

Note that the combined maximum power rating is the only significant difference between the the 500 and 600 models. The individual rail differences are almost insignificant ? just 36W more for the 12V lines. It may be interesting to closely examine the output specs for the S12-430. Here, the 12V lines are significantly lower, but while the +3.3 and +5V individual lines are the same 30A as in the bigger models, the combined maximum for those lines is significantly lower too.

SPECIFICATIONS: Seasonic S12-430
AC Input
100-240V ~7A 50/60 Hz
DC Output
Maximum Output Current
Maximum Combined


Opening up the either the S12-600 or S12-500, one is greeted with an impressively large pair of unique heatsinks. They are both dense and quite large, with a double row of fins. They resemble teeth on a coarse comb. The basic design originated in the Super Tornado; it is a clever way to maximize cooling surface area in the reduced height available to components due to the 1″ depth of the 12cm fan.

Big HS fins reminiscent of teeth on a coarse comb.

Side view show components tucked under HS fins.

The other side is where the cables are terminated.

This 7-blade medium-speed ADDA fan has replaced a 5-blade Yate Loon 120mm
fan used in earlier versions of the S12-500 & 600.

As with the S12-430, cabling on the 500 and 600 is twisted to minimize EMI.

All the output cables are twisted for reduced EMI.

There are a total of nine cable sets. The main ATX cable seems a bit on the short side at 16″, but it should reach most motherboards in most cases.

  • 16″ cable for main 20+4 pin ATX connector.
  • 26″ cable with two 6-pin PCIe video / SLI connectors
  • 18″ auxiliary 12V connector
  • 19″ auxiliary 4x12V connector (for dual CPU boards)
  • 33″ cable with three 4-pin IDE drive connectors and one
    floppy drive power connector
  • 27″ cable with two 4-pin IDE drive connectors and one floppy drive power connector
  • 2 x 24″ cables with two SATA drive connectors each
  • 21″ cable with 3-pin PSU fan speed monitor connector for motherboard

Easy-off 4-pin connector.


For a fuller understanding of ATX power supplies, please read our article Power Supply Fundamentals & Recommended Units. Those who seek source materials can find Intel’s various PSU design guides, closely followed by PSU manufacturers, at Form Factors.

For a complete rundown of testing equipment and procedures, please refer to the
SPCR’s Revised PSU Testing System
. It is a close simulation of a
moderate airflow mid-tower PC optimized for low noise.

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 precise 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.

Great effort has been made to devise as realistic an operating environment for the PSU as possible, but the thermal and noise results obtained here still cannot be considered absolute. There are far too many variables in PCs and far too many possible combinations of components for any single test environment to provide infallible results. And there is always the bugaboo of sample variance. These results are akin to a resume, a few detailed photographs, and some short sound bites of someone you’ve never met. You’ll probably get a reasonable overall representation of that person, but it is not quite the same as an extended meeting in person.

REAL SYSTEM POWER NEEDS: One very important point is that the while
our testing loads the PSU to full output (even >600W!) in order to verify
the manufacturer’s claims, real desktop PCs simply do not require anywhere near
this level of power. The most pertinent range of DC output power is between
about 65W and 250W, because it is the power range where most systems will be

working most of the time. To illustrate this point, we
recently conducted system tests to measure the maximum power draw that an actual
can draw under worst-case conditions.
Our most powerful P4-3.2
Gaming rig drew ~180W DC from the power supply under full load ? well within
the capabilities of any modern power supply. Please follow the link provided
above to see the details. It is true that very elaborate systems with SLI could
draw as much as another 150W, but the total still remains well under 400W in
extrapolations of our real world measurements.

SPCR’s high fidelity sound recording system was used to create MP3 sound files of this PSU. As with the setup for recording fans, the position of the mic was 3″ from the exhaust vent at a 45° angle, outside the airflow turbulence area. The photo below shows the setup. All other noise sources in the room were turned off while making the sound recordings.

Ambient conditions during testing were 21°C and 18 dBA, with input of 120 VAC
/ 60 Hz measured at the AC outlet.

The results of the testing were so close between the two samples that they might as well have been identical. The differences were typically within 1%. Rather than clutter up the article with two complex charts that have the same data, the two sets were combined. The worse of the results obtained for the two samples are presented here. Naturally, only the S12-600 was tested at 600W.

Seasonic S12-500 / 600 TEST RESULTS
DC Output (W)

AC Input (W)


Intake Temp (°C)

PSU Exhaust (°C)

Fan Voltage

Noise (dBA/1m)

Power Factor

NOTE: The ambient room temperature during testing
varies a few degrees from review to review. Please take this into account
when comparing PSU test data.

* Only S12-600 tested at 600W load.


1. VOLTAGE REGULATION was excellent, within -/+2% on all lines at all test loads, except for the 3.17V reading at full powerful, which was -4% off. The low and high voltage seen on each of the main lines is shown below. Unless otherwise noted, the lowest voltage recorded were at the highest loads.

  • +12V: 11.91 to 12.12
  • +5V: 4.90 to 5.02
  • +3.3V: 3.17 to 3.32

2. EFFICIENCY was excellent, as expected of these 80 PLUS certified power supplies. The efficiency / power output ratio curve was quite
flat from below 20% of rated load all the up close to maximum power. The flat 87% efficiency obtained from 200W to 400W is most impressive. In practical applications, these PSUs will be very tough to beat for energy efficiency, with their combination of high AC/DC conversion efficiency and active PFC.

3. POWER FACTOR was just about perfect across the power range.

4. TEMPERATURE: The high efficiency combined with the large heatsinks and effective airflow in these PSUs to provide the best in / out air temperature rise recorded in our PSU tests. At all power loads of 250W or lower, the temperature rise was only +3°C. It gradually rose to +7°C at full power load. This compares very favorably with many PSUs that hit +7~10°C in / out temperature rise by 50% load. It is not unusual for 15°C to be exceeded at full power loads. This means that the S12-500 and S12-600 are very effectively cooled and overheating should rarely be a cause for concern.

5. FAN, FAN CONTROLLER and NOISE: The test environment is live, so
readings are higher than would be obtained in an anechoic chamber readings, due to reflections and reinforcement of sound waves off the walls, ceiling and floor.

The start SPL of 21 dBA/1m was 3 dBA higher than that measured on the original version of the fan-cooled PSU champion (for noise), the S12-430. But it was still extremely quiet. The new Adda-fan equipped 430 is only one decibel quieter. (See postcript to S12-430 eview.) The first hint of fan noise increase was heard (and measured) at 150W output or ~31°C intake temperature. The overall noise stayed quite modest until past the 250W load. When listened up close. the dual ball bearing fan has a bit of the typical ball-bearing chatter, but it is very subdued, and based on our recollection, much quieter than the earlier 5-blade Yate Loon fans first used in these models.

Like the S12-430, the fan controller in these high power PSUs showed exemplary behavior. The ramp up of the fan as load increased was gradual. Compared to the S12-430, the overall noise level was typically 2-3 dBA louder through much of the power range. As the power load went past 300W and the fan voltage climbed beyond ~8V, the higher capacity of the medium speed in the 500 / 600 began to make a bigger difference ? in airflow and the resulting turbulence noise. For those who have a need for such high power capability as offered by the S12-500 and 600, the increased noise at high power is a modest price to pay, especially when acoustics at typical power loads (<300W, even for high power gaming rigs) is so well behaved.

In actual use inside a typical modern PC, we expect these PSUs to rarely ramp up beyond ~30 dBA/1m. Extended high loads are required for the temps to rise high enough to cause further ramping up of the fan.

MP3 Sound Recordings of Seasonic S12-500/600

Seasonic S12-500/600 @ 90W (20 dBA/1m)

Seasonic S12-500/600 @ 150W (22 dBA/1m)

Seasonic S12-500/600 @ 200W (25 dBA/1m)

Seasonic S12-500/600 @ 250W (28 dBA/1m)

Seasonic S12-500/600 @ 300W (34 dBA/1m)

Seasonic S12-500/600 @ 400W (38 dBA/1m)

Some low frequency resonance creeps in at >30 dBA due to the wooden test box in which the PSU is mounted while tested.

Sound Recordings of PSU Comparatives

Seasonic S12-430 @ 150W (19 dBA/1m)

Seasonic S12-430 @ 200W (22 dBA/1m)

Seasonic S12-430 @ 250W (26 dBA/1m)

Enermax Noisetaker
600W (2.0) @ 150W (27 dBA/1m)

Enermax Noisetaker
600W (2.0) @ 200W (30 dBA/1m)

Enermax Noisetaker
600W (2.0) @ 300W (35 dBA/1m)

S12-430 recordings are of the original Yate Loon fan version.


These recordings were made with a high
resolution studio quality digital recording system. The microphone was 3″ from
the edge of the fan frame at a 45° angle, facing the intake side of the fan to
avoid direct wind noise. The ambient noise during all recordings was 18 dBA or

To set the volume to a realistic level (similar to the original), try playing this Nexus 92mm case fan @ 5V (17 dBA/1m)

file and setting the volume so that it is barely audible. Then don’t reset the volume and play the other sound files. Of course, tone controls or other effects should all be turned off or set to neutral. For full details on how to calibrate your sound system to get the most
valid listening comparison, please see the yellow text box entitled Listen to
the Fans
on page four of the article
SPCR’s Test / Sound Lab: A Short Tour.


The new and improved S12-500 / 600 power supplies find Seasonic at the top of their game. These high power models pick up where the S12-430 leaves off and continue on quietly, steadily delivering power on demand. Tops for efficiency, for low noise, for stable high power delivery, and for the minimalist approach that strikes a chord of quality for many users.

Our own testing confirmed that the 500 and 600 do indeed reach 80% and better efficiency at 20%, 50% and 100% loads demanded for the 80 Plus program, which has certified both models. The 80 PLUS test results are available as downloadable PDF files and worth a careful examination. So far, Seasonic appears to be the only PSU brand with a retail presence to have achieved 80 PLUS approval.

While they do not plumb the quiet depths the way the original S12-430 did, the 500 and 600 are nearly as quiet at low to medium load and can take on any PSU of similar power capacity without any acoustic handicap. In fact, the reverse is true: There is not a single PSU we know of that can produce so much stable power as the S12-600 and stay as quiet. At the more likely loads of <250W, the noise level stays well in the mid-20s (in dBA@1m), which is competitive with the majority of quiet PSUs.

We wrote at the end of the original S12-430 review that about the only thing more a gamer might ask for is support for the 6-pin power connector used by power-hungry PCIe VGA cards. Two such connectors are now available in the S12-500 and the S12-600. If you seek quiet, stable, high power without flash, look no further than the S12-500 and the S12-600.

Our thanks to Seasonic USA for the S12 samples.

NOTE: A postscript has been added to the Seasonic S12-430 review to investigate the effects of the change to the Adda fan.

POSTCRIPT: Efficiency Correction
October 22, 2005

Recently, we discovered that our power supply testing equipment and methodology were providing erroneously high efficiency results. In general, the biggest errors occurred at higher
output load points above 300W. At lower output levels, the efficiency error
was often no more than one or two percentage points. No other tested parameters were significantly affected.

Through a fairly arduous process of discovery, analysis and old fashioned problem solving, we modified our testing equipment and methodology to improve the accuracy of the efficiency results and described it all in the article SPCR’s PSU Test Platform V.3. As part of this revision, we re-tested most of the power supplies on our Recommended PSU List. In most cases, the same sample was used in the second test.

The corrected and original efficiency results for all the re-tested PSUs are shown in in the article, Corrected Efficiency Results for Recommended Power Supplies. The relative efficiency of the tested power supplies has not changed.
If the tested PSUs are ranked by efficiency, the rankings remain the same whether we use the original results or the new results.

data is also being added to relevant reviews as postscripts like this one.

CORRECTED EFFICIENCY: Seasonic S12-500 / 600 Active PFC F3

Target Output










Actual Output



In this case, our original efficiency calculations were 2~5% too high through to about 200W output. Above that, the the error kept increasing with rising output power till it reached 8 percentage points off at 400W load. The new figures show that these models are still very high efficiency, but never reach past 82%, which is in line with Seasonic’s own specifications.

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