I have crossfire x1950, 6600, 4gigs ram and all that on 400W. But it's silwerstone :) So you do not need many watt power, new graphic cards are only using less. For examle 3850 is using 120w, while 8800gts up to 230w
with +12 very stable 12,02 - 12,04. So, my advice is to buy some brand names.