Originally Posted by Blindsay
Question though about that then. If you look at 80+'s website, for all of the classes, the highest efficiency % is always at 50% load. are they lying?
You're comparing the answers to two different questions.
First of all, the max efficiency a power supply reaches depends on the design and load levels. Often times it's not really 50% of rated capacity, but maybe 38%, 64%, whatever. It depends also on the distribution of loads (how much on +12V compared to +5V and so on) as well as temperature and input wall voltage. But yeah, if you want to find the maximum for a given power supply, it will be around 50% usually.
If you're running your computer at some power draw at some kind of continuous load that is 50% of your PSU's rated capacity, then great.
Most people are talking about sizing power supplies and looking at how much power their computers could
draw. If max draw goes up to 50% only, then in a game it might be more like 20-40%, at idle, down way below 20% in the "omg the efficiency sux relatively" range. For a computer that doesn't spend most of its time drawing near max power, it would be more efficient to get something where the max draw is more like 70-90% of rated capacity, depending.
But anyway, a few percentage points difference in efficiency is hardly a big deal compared to the total draw, not to mention everything else that draws electricity. That is, unless maybe you're buying power supplies for your server-room folding farm.