Read PSU101, tell me if I've got this right.

Very informative forum here, btw!

OK, my current PSU is a several years old Antec True Power 480W, with a single +12V rail that can supply 22A max output, probably less on a continuous basis with other devices drawing power. This PSU has served me well up to now, but I'm soon adding a GeForce 7800GS AGP card that is going to need 20A just for itself. As I understand it now, that is perilously close to the limits of what my PSU can comfortably supply it. On the other hand, a newer PSU with say, 430W power but two +12V rails supplying 17A each for a total of 34A is more likely to supply all the juice I'll need. Even though the rails are separate, the combined amps are available to all devices hooked up to the system. Correct?

Thanks!

Yeah you cannot combine the rails, usually on the PSU label you can see the actual combined output...

On a side note, seems like your PSU will do fine!

Ah ha, I made a big mistake reading the specs for the card. I thought it said the card needed 20A, but that was just the recommended amps for the 12V supply, which I'm over. Thanks for the link to the graphics card power requireds, very helpful!

I used that PSU Calc first thing, came out at around 275W with my current video card (ATI Radeon 9800 Pro) and 282W with the 7800GS. I wasn't quite sure how related to my exact amperage requirements (282W / 12V = 24A?). Anyway, thanks again for all the help, I will see how this PSU does with the new card!

Thanks for taking time to help me understand all this!