How bad does effeciency get below 20%

[ColKurtz]

I'm getting a new case and new PSU shortly. It's primarily a home file/media encoding server - C2D e6600, 6 hard drives now, maybe 8 in the future, PCIe RAID card, and a PCI tv capture card. I don't game on it -- its using the Intel 965's integrated X3000 graphics. A power calculator I used put my recommended PSU size at 438W, and that's peak. There's enough deals going on at newegg that I can spend about $50 on a good 450W PSU, and maybe $75 on a good 600W PSU (one example).

I'm inclined to go with as high a wattage power supply (tier 3 or better) as possible for around $50 - $75. I'm looking at 80PLUS rated power supplies, but I see the 80PLUS standard measures at specific load intervals, the lowest being 20%. Does anyone know how bad power factor drops below 20% -- in quality PSUs? If an idle load is is 73% effeciency in a 610W vs. 82% in a 430W PSU, then I don't really care... but if it's 59% vs. 82%, that might push me to a lower wattage PSU.

Any enlightenment is appreciated.

 

[jonnyGURU]

The answer to your question COMPLETELY depends on the PSU.

For example: The BFG ES-800 is still over 80% efficient as low as 10%. The Enermax is still around 80% or high 70's at 10%. Most others (like your "one example") are around 70 to 75%... Only a really "old design" would drop below 70%.

THAT SAID... You're only talking about a $2 to $3 savings at the end of the year if you're running 24/7.