Im using a IBM DPS-2000BB (2000W PSU). im measuring the power draw from the wall using a voltcraft energy logger 4000.
Ill post some results im getting later.. but till now the efficientcy is quite dissapoiting.. o ps my psu is around 0.96 Cos Phi regarding efficientcy of the unit it a realy good PSU and not putting out a lot of heat so that means its efficient!
Are you using it for a single board?
It is a great psu and I have 8 of them waiting but a single undeclocked board might be a too small load, see here (it is for the 2500W one but they are similar):
http://www.rcgroups.com/forums/showpost.php?s=ff664b0f8735ce2a9c40796f40b57c49&p=18117345&postcount=611It would be great if you could measure volts and amps at the 12V rail or if you could add more load to the psu if you are using one board.
If that is not the case it is strange, crappy voltage regulators should get way more inefficient as the load increases exagerating the advantage of the underclocking so it can't be that. Having less capacitors might increase the ripple, overshoot and undershoot but it shouldn't wreak havok with the efficiency. The only way I can picture the dc-dc converters drawing a lot of extra power due to having less capacitors and it being more noticeable with more underclocking is if marto increased that dc-dc converter frequency a lot to compensate for the loss of capacitance and that forced him to increase the gate drive of the mosfets to insane levels wasting a ton of power driving them. I have done that wasting up to 20W per mosfet in a high voltage generator but it required a discrete gate drive circuit, I have never seen anything like that in computer hardware and it would be insane if you cared about efficiency or even cost as caps are cheaper than building discrete gate drives.