Hey folks. I recently bought a GTX680 for my PC. Figured it was time to upgrade from my HD Radeon 5850. However I have a question regarding my PSU considering this is the first time i've ever upgraded a card manually.

The GTX680 says I need a min PSU that has 550 watts with 38 Amps on a 12v rail.

My PSU has the following specs:

Model: FSP750-80APG; input rated 100-240V~, 10-5A, 50-60Hz; Output rated (DC) +3.3V/30A, +5V/30A, +12V1/18A, +12V2/18A, +12V3/18A, +12V4/18A, +5Vsb/3.5A, -12V/0.5A, (+3.3V & +5V = 170W max.) (+12V1 & 12V2 & +12V3 & +12V4 =648W max.), Total output power : 750W.
Open Frame, Power supply, input and output rated as follows: (Evaluated to operate up to 3000 m above sea level.)

Obviously I have the 550 watt part covered, but my question is do I have to have 38 Amps on one singular 12v rail? It looks like this PSU has four 12v rails with 18 Amps on each. Do they count as single rails, or do they all come together and combine into a 72 Amp rail.

Just want to make sure I don't do something stupid and not have a proper PSU.

The four 12V rails are really one 12V rail. Even if that wasn't the case, there are two power connectors from the card and they can go on different rails. The requirements are high because of poor quality PSUs that don't provide the stated power, but your whole system power consumption with the GPU loaded won't exceed 400W; the GPU alone won't exceed 200 probably. It should be fine.