Are manufacturer AC cables good enough?

I think I’ll trust the engineers over self proclaimed subjective experts. If a mains cable affects the sound of an  amp it's measurable if it isn't then whatever effect it does have couldn't be enough to make it audible.

I keep telling you guys the manufacturers are always the last to know. That’s just the way it goes sometimes. 

I think the accountants pick the power cord not the engineers 

If the accountant picked the mains cable then the company would go with a very exotic audiophile cable they could produce for $10 use the pseudoscience gobbledygook talk of other high end cable " manufacturers " and give the wide eyed audiophile a bargain for a measly extra $500 with the purchase of a $10,000 amp. Of course it would be voiced especially for them 😉

Ayre for many years had a line of Ayre branded premium cables manufactured by Cardas if my memory is correct.

Yes, the "Ayre" cables were sourced from Cardas. I think the speaker cables were essentially Golden Reference but in a different jacket. Looks like Ayre no longer offers these (judging by their website).

My thinking is that Ayre wouldn’t supply cables that are inadequate for their components.

Ayre would probably say that their OEM cable is "adequate" but add that you can get even better results with some aftermarket cables. I know they often show with Cardas, sometimes Audioquest (maybe others?). From their perspective, it isn’t sensible to include a $$$ power cord or IC with their components. For one thing, as was pointed out up-thread, they have no idea how long your cables need to be. Secondly, tastes and opinions of cables widely range. Some don’t think cables make any difference whatsoever while others insists on specific brands or technology. It would be tough to satisfy more than a minority of customers, and that's assuming the cable is even the proper length.