Thanks. You want to know something? The stock PSU that came with the case doesn't have this issue. I'll still need a 500w or more so I'll check out what you recommended.
You probably won't to tell the truth. Look at the power ratings, CPUs don't need more than 150W at the most, G cards 80W HD's only need a few and fans need very little. There are calculators out there if you search. Most systems are sub 300W, but by selling higher rated PSUs they can charge even more money.
If you're not running SLI, or more than four HDs then you might well only need 300W. For a really high power system you might need 400W for comfort and to deal with a high peak load at startup, but more than 500W is taking the piss.
Spend the money on a reliable brand, the truth is that cheap powersuplies offer to source 400W and fall over and die at 200. Seasonic, Antec, Zalman, FSP are ones to look for. An excellent PSU is the Seasonic 12 range, very efficent so there isn't much excess heat generated and damn near silent operation.