i just checked the fortron link out and the specs of the fsp530.
doesnt give any info about the 3.3+5 volt lines, so maybe it is safe to assume that all the lines can operate at max capacity without exceeding 510v in total.
although the "peak power and current shall be supported for a minimum of 15 seconds" makes me think that the PSU will give out after that. dunno. i mean the max power is within the rated specs, so why not?
so, yeah, maybe you are correct when saying that the 3.3 and 5 volt lines are close to 296 volts, there are no contraints on those lines, like that on the 400 watters.
on a side note, i was also looking to pick up a new PSU. saw some nice things said about the antec 550 and the ttgi 520. after seeing this fortron, its getting harder to make a decision which to pick up. the fortron is very attractive due to the price and numbers it puts up.