12 ga wire can carry 20 amps, so as far as "size" goes, anything larger is simply a waste of money. There is no benefit in hooking up a cable that can provide more power than your equipment is abel to use? As for design, shielding, covering, flexability, the devil is in the details. Have a look at the cables made by Puritan out of the U.K. Intersting design and as floppy as a wet noodle. Just one suggestion.
What size power cable?
How “big” does a power cable need to be for upstream components? I get that amps can benefit from a large cable to carry plenty of current, e.g. 8-11 awg. Although my preamp and phono preamp have robust power supplies, they can’t possibly benefit from such capacity, can they? Extreme overkill is the norm in hi end, but is there any benefit to more than 12 or 14 awg on a preamp or phono preamp? Much less digital components.