Electricity usage of a 1200w Power supply

[XZR]

I'm planning to add a 1200W PSU, just mainly to future proof it, I don't think I would need that much, probably use only about 700w.

I do plan on having 2x 5870 radeon cards in crossfire
sound card
5-1 memory card readers
etc etc

but I'm worried about the power bill.. Will having a 1200w power supply but only using 700w give me a huge bill?

or it wont be any different to a lets say 850w Psu?

Thanks guys

[burebista]

The PSU will draw from the wall exactly how much your rig need. So if you need 700W from your rig a 1200W PSU will draw same 700W (in fact ~875W AC assuming 80% PSU efficiency) as a 850W PSU.
But you won't need 700W DC from your PSU for HD5870 Crossfire. Only (http://www.xbitlabs.com/articles/video/display/radeon-hd5800-crossfirex_10.html#sect0) if you're a heavy overclocker and you "play" a lot Linpack and Furmark with a Nehalem. :D

[EarthDog]

Corsair 850TX/HX should fit that bill with plenty to spare.

[johan851]

1200w is way too much, even for future proofing. EarthDog is right - an 850w should be more than enough, and a lot cheaper. Probably quieter and better quality, too.

The wattage rating on a power supply is its maximum output. It will only pull from the wall what the system pulls (plus a bit of extra wattage that gets lost in the AC->DC conversion). A system that pulls 100w will pull about 120w from the wall regardless of whether you're using a 200w supply or a 1200w supply.

I would recommend you read up on the actual power draw of computers. I think it's lower than you might guess.

[Psykoikonov]

just thought I'd drop a couple links to JohnnyGURU (great site for power supply reviews).

Corsair HX850 850W review (http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=153)

Corsair TX850 Power Supply review (http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=126)

The efficency is better on the HX than on the TX. Guessing your system will use around 500W (at load) the HX will consume 566W (AC) @ 510W (DC), where the TX wil consume 613W (AC) @ 521W (DC).

Other option would be the OCZz Z Series 850W (http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=167)(gold rated) which at 500W (DC) consumes only 555W (AC), however may be quite a bit more money than the HX. The efficiency of the OCZ at low load is still very respectable where most PSU's efficiency falls off quickly.