Power Supply question

[littlej]

Loads on the rails, found using this: (http://www.extreme.outervision.com/secure/psucalculatorpro.jsp)

+3.3V +5V +12V
8.6 A 32.4 A 33.7 A

What I'm confused about is the 5V rating. Even on enormously powerful supplies like Thermaltake's 1200W Toughpower, the amperage rating looks like it's only barely enough with what I have.
Its rating is 30A @ +5V and 3.5A @ +5Vsb. Adding together those amperages puts it at 33.5A.
Am I crazy, or is that huge power supply only just barely providing what I need?

[Hagar]

Most of the power in a PC is taken from 12V. There is no need for more than 30A on 5V, most PC's use a lot less. So the difference between a small PSU and a big one will be the 12V rating. There is more than one 12V output.
5Vsb is the standby supply, it is separated from the normal 5V.

[littlej]

I went ahead and got the 1200W ToughPower (got a deal on it, only ~$260). I figure it'll be worth it someday when I upgrade video cards in the future.

I found out that the calculator I was using was being pretty conservative, by estimating the loads based on all components running at 100% simultaneously (a highly unlikley but possible scenario).
I re-estimated with everything at 100% except my optical & floppy drives, since I can't see how I'd be using all three at full power simultaneously with everything else at full power also, and got a 5V amperage of 25.6A.

I used to have a 600W Noisetaker I, and suddenly one video card stopped working, and I thought the card died, but I kept it in, mostly because I didn't feel like tearing apart my cooling circuit. Then a few months later, the PSU died completely. I replaced it with the 600W Noisetaker II and the "dead" card magically came to life again.
Now, the same thing has happened, with a video card, except it hasn't died completely yet, hence the reason for a new PSU.

[Hagar]

Load balancing can be an issue when there are two video cards, as each rail may have a 20A limit.
There is some good PSU info on this site: http://www.playtool.com/pages/psuoverload/overload.html