We've got 6 computers in our house, 2 of which are high powered gaming/media machines. We've got an xbox, an xbox 360, and 2 PS2s. 5 televisions. Oh, yeah, a bigass server that runs continually. 4 kids, each with various personal electronics. On the weekends, all 4 gaming systems and at least 3 computers are running at any given time.

My 400w hps is the least of my worries.