12v amps for crossfire?

[JigawattPSU]

I'm sorry if this is a newb question that has already been answered, but i just want to make sure. I plan to get another HD6770 and crossfire it with my current one and i will be needing a better PSU for that since my current one has just one 6pin connector anyway.
I'm considering a 750w PSU from a local computers store, but i'm afraid it might not handle my overclocked pc.
Here are the amps for each line:
+3.3V: 28 A
+5V: 28 A
+12V1: 20 A
+12V2: 20 A
+12V3: 20 A
+12V4: 20 A
-12V: 0.8 A
+5VSB: 2.5 A
I used the eXtreme PSU calculator site to calculate my overclocked q6600 wattage and got a result of 199w and afaik the HD6770 draws up to 108w.
Now correct me if i'm wrong, but the 6pin connector can supply only up to 75w? So 108-75= 33w for each card via the pci-e slot as a minimum. So that would mean that during intensive gaming with both cpu and gpu at peak load there has to be 66+199= 265w via the motherboard? Is 20A on the 12v enough in this case? I'm afraid of ending up short by some 25w.

 

[EarthDog]

The 6770 is a LOW powered card. Honestly, Im sure you can get a molex to 6 pin connector on your current PSU could be just fine. What is the make/model/wattage of your current PSU? My suggestion is to look at the PSU guide (link in my sig) for QUALITY PSU's in the 550W+ range for that system.

As far as your math you are looking in to it WAY to deep with different rails and such/mobo... etc. The mobo feeds off the 24 pin/8pin plugs and are likely on a different rail (if the PSU you are looking at is actually a multi rail unit).

 

[JigawattPSU]

Well for one thing my current PSU is a 550w Xilence that i'm pretty sure won't handle another HD6770
3.3V 30A
5V 32A
12V1 18A
12V2 20A
-12V 0.5A
5VSB 2.5A
and the other thing https://bitcointalk.org/index.php?topic=51740.0
i don't want something like that to happen in my box :\

 

[EarthDog]

Id be more worried about the quality than the wattage... but yeah check out the guide.

 

[Bobnova]

If it can actually put out 550w it'd be fine.
Whether it can or not I don't know. I'd tend to guess not.

 

[JigawattPSU]

Well i found a nice article about psu's on tom's hardware that named several crappy psu brands including Xilence. Quote "Lack of protection circuits, low efficiency, and bad build quality were major points of criticism."
My guess is even if my current PSU can handle the upgrade i'm planning it will likely significantly shorten its lifespan to the point where i could end up with blue smoke and a ruined PC in a year or less.
Anyway i decided to get myself a corsair cx600 which should be enough.
Here are some PSU calculator results.

 

[woboy]

Volts X Amps = Watts. Each PCIe X 16 is capable of supplying 75 Watts.
CX600 12 Volt = 40A = 480 WATTS.

The Corsair is a good power supply, but is an entry level product.
You might consider, if you are in USA, on newegg, the Rosewill Capstone 550 Watt power supply
45.5 AMP on the 12 volt = 546 Watts, Gold efficiency, and modular cables for $75.
A very good Super Flower unit.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817182262

The CX600V2 is out of stock on newegg, was $71.98 shipped before $10 MIR.
Amazon $76.59 shipped http://www.amazon.com/Corsair-CX600...e=UTF8&qid=1347490097&sr=8-3&keywords=cx600v2

The Rosewill Capstone 450-M has 37 Amp on the 12 Volt for 440 Watts.
Modular/Gold $69.99 - 20% discount (EMCNANC35 ends 9/13 $56)

 

[JigawattPSU]

I wish i was in US. The PC parts i tend to get are usually cheaper on newegg and amazon than what's available at the local stores or on ebay from european sellers.
Anyway the Corsair i'm about to buy will have to do, it's like the best thing available here for the price which is about 85-90 USD.