Ok you REALLY don't know what you are talking about.
I have a 600 watt power supply and my computer runs fine. My computer is a high end, $1000 computer.
What?
Look. Do you know the power of TWO radeon 6850's PLUS the power of i7 990?
That can come to around 800 watts. It will work with anything above 600 but it's not recommended because they might heat or move slow.
Your PC runs fine because your processor and video card isn't a pain in the ass energy eater.