Hi,
If this is the same system you were talking about in this previous thread:
thread779-1033733
then, while it probably won't hurt you to get a different power supply, I would caution you to at least be prepared for the possibility that the new power supply does not solve your power switch problem. Unless you have a lot of gear you didn't list above, I would think that an Antec 400W supply should be more than sufficient. Unless your power supply has a failing circuit and is causing your problem, replacing it with another 400W PS or even a bigger one will not fix the problem. Replacing it would be one way to possibly rule out the power supply as the cause of the problem, but if the PS is not the source of the problem (and a fully functional 400W Antec should be enough for your system, but...) then replacing it won't fix what's broken. On the other hand, if the problem is a PS failure (or even just a hardware brown-out of the power switch detector voltage) then a new 400W Antec should fix it.
I had shut down and other problems with my new AMD system, and upgraded from the Antec 380 to the Antec 480. Result: the hang-at-booting-from-CD-ROM problem went away, but the shut down problem remained. My +12v lines were closer to +12v, which I think explains why the boot-hang problem was fixed. But the shutdown was either the motherboard, or the installation of the CPU. AMD processors are designed to shut off the power supply if they go above a certain temperature. This is in the chip and is independent of the BIOS if I understand correctly. Part of my solution was to find the Arctic Silver 5 website and read up on how they recommended using it. Turns out their recommended installtion procedure was different from what I had done the first time, which might explain my shutdown problem.
I'm just suggesing you consider the possibility that your problem may not be the power supply, despite all I said in my previous post, and all that has been said above in this thread. On the other hand, it could be. If you can afford to replace the PS, go ahead and do it, a stronger one probably isn't necessary, but it probably won't hurt anything (besides your pocketbook) and it may solve the problem, but who am I to say? It may be emotionally helpful to consider that the problem may be elsewhere before you hang all your hopes on the PS. If you still have the same problem with a new power supply, then the PS wasn't the problem.
I don't know what kind of current the Radeon 9100 pulls, but I'm guessing that it pulls quite a lot. It might even pull enough to cause me to reconsider all I've said about a 400 being strong enough. If you had a known good supply you could borrow to test the system with before buying a new one it could potentially save you some grief.
So the answers to your questions are, yes, probably and maybe. Yes Antec is good, yes a 400 is probably strong enough, but who knows? Maybe replacing the power supply will fix the problem. Maybe it won't.
(I know, this is almost about as helpful as saying nothing at all.)
--torandson