But my confusion stems from how the PSU has three 12 volt rails but only two PCI-E connectors. I am assuming that a 12 volt rail goes to each PCI-E connector, is that correct? But then if you read the specs for the PSU it says:
1 x 12V(P4)
1 x 12V(8Pin)
2 x PCI-E
So does this mean two of its 12V rails go to the 12V(P4) and the 12V(8pin)? Where does the third one go?
on that power supply one 12v rail 12v and the 12v atx 4/8 pin are the 24 pin atx cable and the 4/8 pin pci power plug. there on on main rail. it looks like the pci video power plugs are on one rail each. with a video card spec they give a max reading if someone was to game or over clock the cards...not all power supply as built as well as others. the video card vendor use that min wattage as the max the video card may draw.
All of those 12v rails are perfectly fine. Remember; the card draws up to 75 w alone from the pcie slot and will be fine with 22a on the 12v rail. Hell, you'd be fine with18a each rail such as my psu that powers sli 570. The new radeons dot draw as much power as their predecessors per performance.the 7850 for exampledraws 75wfrom the pcie and 75w from the 6 pin.you could have a 10a rail and be fine