If you have 4 12v rails w/ 25A on each rail, you still only have a total of 25A available, not 100A.
If you used your theory on the above mentioned example, you would have 1200w available on the 12v rail
I'm sure it's in Jonnyguru's FAQ, let me get to the other box and I'll look it up.
From the above mentioned FAQ:
Ok… Now look at the 12V rails. There’s four 12V rails (I’ll explain why later) and they are rated at 22A and 22A, 36A and 36A. The maximum combined wattage of those two rails is 65A (780W / 12V = 65A).
What?!? But 22A + 22A + 36A + 36A is 116A? Like the +3.3V and +5V rails I just mentioned, +12V rails are not additive. You can load each one up to 22A or 36A, but you can’t load them all up to their max.