is this the part you're referring to
"The requirement listed by NVIDIA is 26A of +12V current. To adequately power the card, and at the same time adequately power the rest of your system, you'll need a PSU with a total output of 550W or more"
the 26A is for the total configuration, not just the video card.
same goes for this
"1. Does your power supply meet the minimum power supply requirements for the 8800GT? Wich is: 400W and 22 Amperes on the +12V rail(s)."
well considering the total power of your power supply is 650, there is no way it would handle both the rails at their peak output... (that'd be 672w alone for the 12v, leaving everything else starved for power, 3v. etc.) same goes for the OP not being able to run all 3 rails fully loaded... I just saw he has 3 rails and not 2, so if he could move it to the other rail not being used by the cpu (i'm guessing another pci-e connector) that would be a good way to test.
according to nvidia's site, the 9800gtx uses a max of 140w (just the card). 140/12=11.7A Technically, yet the RAIL of your PSU is capable of supporting the cards, even the 26A, since the cards would be using 23.4A but that's if all that's on the rail are pci-e connectors and nothing else drawing power. the cards would have been using 280w peak of the available 650w of your psu. leaving 370w for the rest of your system. Which should be plenty for your config as my 400watt psu is running everything in my specs just fine on a 22A single 12v rail. so your psu technically should have ran 2 9800 or a 9800gx2, which actually uses less power than 2 9800s at 197w or 16.42A. (again going by the numbers on nvidia's site... if your rig didn't handle the load then either the brand of the particular cards used more than the nvidia ref., nvidia lied, or your psu isn't as strong as it used to be?)
Its true that his PSU may not be capable of the full 18A, but then again he doesn't need 18A for the video card itself, since the card itself draws around 9amps. At least i hope antec power supplies don't loose %50 of their capacity in 2 years cause the one i have now is even older
seeing as he does have extra rails, he should be able to move it to another rail for testing purposes. I agree that he should replace the psu if its rails are damaged.
edit: of course there is that fact that not everything always works the way it should...