I really don't have enough data to go on here to provide a good recommendation, so I'll go with my gut.
- I can't imagine a good reason to need to put 70A on a single 12v rail.
- there are only two ways I can think of that you could even implement this:
- If the power supply is running a single internal regulator for the 12v rail and you have some sort of current sensing on the individual output connectors, you could then do some kind of current limiting that could be switched on and off. However, you are still running a single regulator so it wouldn't make any real difference to the reliability of the unit, although it might provide some kind of protection to external equipment. Switching off the current sensing (fusing) would allow you to then output more current on any single line.
- If you are running multiple internal 12v regulators independently on each output, then you could gang them all together internally so that you could provide all of your aggregate output power to a single output if you wanted.
Basically, to me this just sounds like a marketing gimmick, as putting that much current across a single output connector is almost guaranteed to cause something to melt within a year or so.
Not to mention the fact that shoving that much current down a single set of wiring is going to result in some significant I2R losses.