I've got my PC up and running, but I'm soon to switch power supplies. (running with a 500W one that is just doing the job). As I can't afford to spend much money, I'm looking for the most efficient PSU I can find. I found this nifty PSU that draws just a tad more than 1600W to output 900W, which means around 55% efficiency (best I could find, most are around 35-40%). As this one is just a little more expensive than the 700W version of it, which also does 55%, I'm wondering whether the efficiency of the PSU increases the further away it is from it's max output (like, putting out 400W it will draw 600W instead of the 727W it would if it was making 55%). So, does PSU efficiency decreases as it gives more power, or it is the same no matter how much power you're drawing of it?