P=(3.3x26)+(5x30)=85.8+150W=235.8W and (20x2)x12=480W
530W (assuming power is right) has too many unknowns. If I sat down could prob figure out something with substitution and the maths I`d rather not use so...lets draw a veil over that, I cant be bothered
580W (assuming current is right)....the numbers are the same.
i`m guessing because of this the current ratings are wrong. Big guess. Cant concentrate at the mo.
I'm not quite following what you're trying to calculate (I've only skimmed over your calculation) but you're not assuming that the maximum power rating is the sum of the max power ratings on each line are you? Because clearly the PSU can't output full power on all rails at once.