Power Supply "Rail" Question

[myketuna]

So I bought this power supply *working fine so far... I think*:

Antec BP550W PSU (http://www.newegg.com/Product/Product.aspx?Item=N82E16817371016)

And was wondering what the +12V rail thing means? Like I hear people say that you need say 20 Amps on the 12V rail. What does that mean? Like mine on the back of the box (and on the specs tab on the site) it says:

+12V1@22A | +12V2@22A | +12V3@25A | -12V@0.5A

So does this mean I have 69 A on the 12V rail? Or does each rail correspond to a certain plug on the back of the PSU? I'm wondering about this because I was thinking of buying a graphics card and if the 25A rail is on a certain plug in the back of the PSU, I'd like to plug my 6-pin PCI-E connector there to give it adequate power. But... I don't have a clue. :D
This applies to all power supplies obviously, but I would like to know what my 12V rail rating or amperage or whatever is, as well as an explanation about the whole subject. Thanks to anyone that can enlighten me. lol.

[air12ick]

Each molex connector (with the yellow wire) usually has a dedicated rail. Usually the higher amperage (25A) on the 3rd rail is reserved for the motherboard, usually the 4pin connector or 8pin connector. The other 2 rails at 22A are the same for a reason. They are meant for the SLi compliance, in which case they are the same amperage because it was designed to have one rail dedicated to each video card. So in your case, the video card you plan to purchase should not exceed 22A.

Also, just if your wondering why the Motherboard needs 25 amps, it doesn't. That 25 amps rail is also split among the other devices in your computer i.e. hard drives, optical drives. Usually Antec provides a simple diagram of where each rail delievers its power.

The -12V rail...I forgot what this was for other than provide a negative terminal for the motherboard.

You do not have a total of 69 amps on a 12V rail. Each rail is seperate, providing its own amount of amperage per "channel" per se. Technically, your max 12V rating is 22 amps, not 25, 44, or 69 amps. So be careful when you purchase your video card.

Hopefully that helps.

[myketuna]

Damn. So I was thinking of buying a nVidia 9800GT and the specs recommend a minimum 400W PSU but then in parentheses it recommends a power supply with +12 Volt current rating of 26 Amp Amps. So... does that mean I'm SOL? If it does, shit. lol. Seems like the only thing this PSU can run would be something like a 9500GT which is.... eh. It'll be a big upgrade from my onboard 8200 graphics, but I really want to get that 9800GT. I DID get a 9600GT like yesterday, but it suffered from the "black screen of death" problem that seems to be pretty prevalent *from searching through various tech forums*.