Referring to efficiency, my current rig: Asrock H61MV-ITX Pentium G620 2x2gb undervolted Micron ram Toshiba 2,5" 5400rpm HDD and one 90mm fan draws 15,3W from the wall at idle with Z2-200-ATX and SS 12V brick(which is efficiency class level V), while with the LITE-ON 250W 80+ Bronze PSU it draws aro...

I'm using Z2-ATX-200 with Seasonic 5A 12V brick, no problems at all.