Are manufacturer AC cables good enough?

Talk to Ayre, ask them does an aftermarket mains cable change the sound signature of their amps, if so why? If one is objectively better why not use it or advise the use of it? What wire do they use inside the amp? Have they tested different mains cables and noticed observable measured differences? If you want to use an aftermarket mains cable I would make sure it has the required safety label from UL or CE to know it’s been tested. For all the blathering about the inky black darks and improved soundstage let's see some evidence beyond testimony. 

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.