Are manufacturer AC cables good enough?

Why? to make more money .

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 😉