> what exactly two AC power cable provides, that one AC cant?
As an extreme: I can have Central Maine *AND* Bangor Hydro *both* bring me power, run duplicate inside wiring, and plug the console into both.
(Yeah, might cost a million bucks to bring a line in from CMP's network....)
Sitting right here, I could have both utility power and generator power. As it is, there's an hour while I wonder if the fix will be quick, then start shutting-off the utility wires, yank-start the gennie (ah, new one has battery! dead yet?), start cutting-over the switching. Good enough for the freezer. Might be a large number of lost ad sales, or emergency announcements.
At Neve's end, it is one more $99 power supply and a few diodes. Or the whole redundant thing can be bought pre-made from PC server power supply bits. Since this is probably not a cheap console, $99 may be a minor (and maybe optional) frill.