It should work fine up to a single 6970 card or a single 570.
-The wattage rating is almost just a "model number" and has little to do with what video cards it can power.
The way power supplies are rated is maddening. physics 101... P=E*I and normally they assume that you do not draw 100% load from all the rails at once.
Pay more attention to the actual amp rating on the 12volt rail. And keep in mind that ones that "claim" to have more than one 12volt rail are usually false claims.
http://www.ebuyer.com/product/191844
£41.76inc. vat Extra Value
CIT 850W Black Edition PSU 12cm Dual 12v CE PFC Model 850UB
If it is powering a pair of 4870's without crashing, then its not too bad.
Two 12 volt rails at 28 amps.. P=E*I 12 x 28= 336watts x 2= 672 watts. Once you add the 3.3 and 5volt rails it is at about 850 watts. So their rating is actually fairly honest.
Someone who bought it commented on the site. Copied/pasted below.
"Review:
Very Nice
review by:Ian rating:
customer ratingoperating system:Windows 7
Bought this for my wifes PC as it now has a 4870 x 2 and needed the extra ummph.
Open the box to be pleasantly suprised by this PSU. It has 4 molex, 4 Sata, 20 + 4 mainboard, 4 pin board and a 6+2 pcie connector and a floppy.
So plenty of connectors for all.
The duel rails have the following ratings.
+3.3V @ 30A
+5V @ 33A
+12v (1) @28A
+12V (2) @28A
-12V @0.3A
+5VSB @2.5A
As you would expect at this price none of cables are braided and are a standard lenght but the do come in sets of 2 (2 molex on 1 cable and so on) so there is some scope for cable management.
The unit istelf is quiet and is doing the job it was bought for.
On a budget this is well worth a look if you need those extra watts."
http://www.ebuyer.com/product/246658
Now £99.69 Antec 900W High Current Gamer PSU
+12V1 - 40 A / 0 A ¦ +12V2 - 40 A / 0 A ¦ +12V3 - 40 A / 0 A ¦ +12V4 - 40
12x40=480watts. But times 4? = 1920watts. A normal 15 amp 120 volt circuit is 1800watts. So at 1920 watts it would actually trip the breaker!! Seems a bit far fetched, so antec's rating is kinda flawed too.
A single 40 amp rail is more believable, since at the wall you must add the other rails and losses. This would mean that the much cheaper 600 watt corsair (48 amp 12 volt rail) is actually more powerful. I am not saying that antec is bad, just that there is no way that rating is correct.
The 520 watt antec you picked out is claiming a single 12 volt, and guess what? It just happens to be a 40 amp 12 volt rail like the "900".
12x40=480 watts, then add the 3.3 and 5volt rails and its actually around 650 watts like the 900 is if you assume its a single 40 amp rail.
I would bet that the 900 is the same power supply with fancy red trim.
http://www.ebuyer.com/product/192111
£59.40 Ocz Fatal1ty Series 550w Psu
+12V1 - 25 A ¦ +12V2 - 25 A this puts it around the same power as the off brand 850 watt.
http://www.anandtech.com/show/3985/three-550w-psus-for-different-prices/8
And it is seen running at 110% load which is good.
http://www.ebuyer.com/product/264380
£49.07 XFX 550W Core Edition Pro PSU
Single, high power +12V rail (up to 53A/636W)
Hmmm so XFX is already just admitting to making one power supply and marketing them as 550 to 850 watts? Antec seems to playing that game too. I believe corsair also does this.
Pay attention to the 12 volt rail amps, try and get one with a high single 12 volt rail amp rating, or 25amps and above if it's 2 rails. Don't believe any have more than 2 rails, because as you can see, the math doesn't allow that to happen.
Also look for reviews to see if that model actually puts out what they claim.
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