You might not suspect it, but a computer can save as much as 10 watts (or more!) of power by using an energy efficient power supply.

DC Power Supplies and Adapters

In general, I've found AC power supplies to be much more efficient even though they require AC-to-DC power adapters (which if I understand correctly actually uses a bit of power by itself), but I've yet to find a reliable power adapter.

PicoPSU

The picoPSU is manufactured by Mini-box.com. Not only is it small, it is incredibly efficient! Don't expect these little guys to power your RAID, dual processor, SLI gaming machine though, they range from only 60 watts to 120 watts. You'll need an external AC to DC adapter as well, kind of like the ones that are commonly used with laptops.

With the PicoPSU, I've seen small motherboards with energy efficient chips (like the via C7) get as low as 15 watts of power consumption without a hard drive.

AC Power Supplies

SeaSonic

I have had good results with SeaSonic power supplies, in that they use less power when plugged into the same systems as other power supplies, measured by the kill-a-watt meter. That's the only way I know how to measure their effectiveness. Their marketing materials report that they achieve very high efficiency, 80% and more for some models.

FSP Group

I just bought some FSP Group "Green" power supplies. I'll report my findings here.

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