welshmousepk :
except corsair.
good advice, but id agree with ulysses that getting a corsair PSU is the best way to go (provided it IS compatible, which i think it should be given thats its an alienware, not a dell branded desktop)
I can't say "best" because there clearly are better PSU's. Corsair makes, I should say sells, a lot of good PSUs(8.5 - 9.5 ratings), and a few great ones....but only the HX series falls into that category and while the HX's do well electrically, they could be quieter. Not a single PSU has yet made the Editor's Choice List at silentpcreview.com though I am expecting that the new Gold Certified HX's which I have seen at the 80 plus site but not yet on the shelves will break that drought.
I am not knocking Corsair.....just making the point that just because it says "Corsair" on it, doesn't mean it's 10.0 .... Corsair has chosen to sell only in the enthusiasts market niche . Other companies have chosen to sell across all market segments .... Antec's SG series or Seasonic X series for example are all 10.0's and every one is on the aforementioned EC list, but Antec / Seasonic also chooses to sell to other market segments where price is the defining characteristic and filling that need doesn't diminish the quality of their SG line. Seasonic, Enermax, Silverstonr and Nexus all have top end models but, like every other manufacturer, not every one is going to be a 10.0
I think the company to watch however is Enermax who has a complete line of Gold Certified PSU's about to hit the streets.