Are manufacturer AC cables good enough?

Why would a manufacturer ever sell their equipment with a poor power cable or a power cable that makes their product sound poor?
No kool aid here.

The problem with talking to manufacturers is that half of them are as inexperienced on this issue as the hobbyists. Ok, well, probably not half. However, it is a shockingly high percentage of them that operate from received wisdom and theory, and have not even done comparisons themselves. I learned I could not simply take a respected manufacturer's word on all matters. They have blind spots, too.  

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.