One of the key criteria to getting a new EPA Energy Star rating on a new computer is having an "80 Plus" power supply. A computer power supply that is more than 80% efficient at 20%, 50% and 100% load can earn an 80 Plus logo. Finding an 80 Plus power supply for a do-it-yourself PC at a reasonable price has been challenging and too many 80 Plus power supplies are oversized and overpriced.
A large price tag prices out a large portion of the market and oversized power supplies don't actually deliver the kinds of efficiencies their marketing implies. A 500 watt power supply that is rated 80 Plus will perform at well below 80% efficiency when paired with a modern PC that typically uses 50 to 100 watts of power because that's less than 20% loading. The solution is to find a small and inexpensive power supply in the 200 watt range and Sparkle Power Inc. may have produced the right solution with their SPI220LE power supply.
The SPI220LE is small (fits in 1U chassis and some MicroATX or FlexATX chassis), reasonably priced at $55 MSRP (available online), and it's completely silent since the fan doesn't even move until you get to 50% loading which is almost never. In my quest to build a 50 watt PC, I hit a point of diminishing returns because my SeaSonic S12 330 watt PSU couldn't operate that efficiently at 15% loading. I could not get the computer to use less than 50 watts no matter how hard I tried and 51 watts was as low as I got.
With the SPI220LE, power consumption on a G33 motherboard and Intel E6750 dropped down to 47 watts when it was 52 watts [UPDATE 1:00PM - using an already efficient Seasonic S12 330W power supply. The 330W PSU while efficient at 20% to 100% loses efficiently at loads of 15%]. A D201GLY dropped down to 31 watts in idle power consumption with the SPI220LE while the same computer measured 46 watts when I used a cheap PSU that came with a $16 MicroATX chassis which meant it was consuming an extra 48% in power. That's a huge difference in efficiency level and it's no wonder the EPA is prioritizing on power supply efficiency when it comes to computers. Now I just wish more vendors carried the SPI220LE power supply so that I wouldn't have to pay full retail price.