You are good.
EVGA specs say 38a and a 550w psu:http://www.evga.com/products/moreinfo.asp?pn=012-P3-1570-AR
If you look at the psu label, it says 540w max on 12v1+2+3. divide that by 12v, and you get a maximum of 45a which is excellent.
Even a GTX580 or 7970 will run with that psu.
Most psu's are really a single rail, with the output leads divided up so they meed UL requirements for safety.
A pci-e slot can deliver 75w maximum, a 6 pin psu lead can deliver 75w max, and a 8 pin lead can deliver 150w max.
The psu leads will have been divided up for you so you don't have to worry about any of that.