PSU for my prospective build

^ The Corsair 650TX can handle the X3 720 + HD 4870 crossfire...
But you wouldn't have the required power connectors...So you would have to get power adaptors for powering 2 cards...

Yea, I remember reading about the connectors. Something about 4-pin I think. It was either here or on a review site. The person said that they didn't like the idea of using adaptors on the cards. What would the problem/disadvantage be?

If my pc pulls 300W, for example, will the power cost be the same with the 650W and 750W PSU?

Hardwaresecrets.com also recommended to choose a power supply that will be working between 40% and 60% of its maximum capacity.

It should work fine, but it's best to use the native connectors.


Should be nearly identical, but it all depends on the efficiency of the particular PSU at a 300W load.


PSUs are most efficient at 50%, so the closer you stay to that the better.

^+1 Explained very clearly...

And make sure you get a high quality 80+ certified PSU like he said, if you want to keep the power down...

I say go with the 750 and avoid adapters.

Is a PSU that is too much power for a pc, and runs below 40% max capacity, less efficient?

BTW, I went on the Corsair site and used their PSU finder and for my system with one HD 4870 they recommended a 450W-550W PSU. For two HD 4870s they recommended a 750W-850W PSU. That's a bigger jump than I anticipated. Right now I plan on only using a single HD 4870. I really don't know if I will eventually CrossFire or if using a single card that comes out several years down the line will require significantly more power than the current crop of cards.

Haha if you like the looks, go for the Coolermaster UCP Ultimate 900w, or 700w if you want

Corsair Modular 750 watt. can pull this thing off with no problems at all.
Its not about watts its about how much amp on each 12V rail can it support and will it provide the current needed at lets say 50degrees PSU temp.

BFG, Zalman, Corsair will give you 80+ certification. awith a 5year warranty.

Cooler master is not the top brand in PSU;s but its good for the money.

Go for Modular 750. i build a gaming rig almost everyday. a 750 can handle GTX295 with ease as well.

BFG is 3, 5 and lifetime warranty for GS/GX, LS/MX, ES/EX respectively. Zalman is 3 years AFAIK. Corsair is 5 years, but 3 for the CX400 and 7 for the HX750/850.

80Plus certification doesn't matter nearly as much as good quality, nor is it an indicator of such.