I love the response, I have no idea what I'm talking about and then.... "There is some inefficiency to account for in most PSUs but certainly not close to 50% on current PSUs. Most PSUs will happily run 24/7 at 80% (or more) of their rated watts. Some good quality PSUs will run 100%+."  If you read any decent power supply review that includes the efficiency curve, you'd know I was talking about the peak efficiency.  Please read up before slamming someone, your response shows you don't know what I was referring to, people that don't know what you're talking about might take your response as educated and I feel sorry for those that might take your word on something you don't know about.  Here's a simple power supply review that shows the peak efficiency is at about 50% (this random review I picked shows 89% efficiency at 600w and 85% efficiency at 1188w, meaning it's losing an additional 4% as heat at the peak power), there are many reviews out there that show that.  http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story3&reid=222