Are manufacturer AC cables good enough?

They’re good enough. My rule is simple. If there’ s a long debate about a tweak. Leave it. Invest in what clearly matters.

About once each year a skeptic is brave enough to try and figures it out. At that rate by the end of the world the debate will be resolved.  ;)

Gosta: Your rule is simple indeed, but flawed. You base it on a debate from other people, AND, you give it a long time to develop. Why not “solve” it once and for all: try something for yourself. Unless you don’t trust your ears, that’s really the only way to know.

And what “clearly matters”? And why is it different than “a tweak”? More importantly, why do you think this “other people” never “invest” in “what clearly matters”? 

A general rule to follow is the more audiophiles’ hair catches fire the greater the odds are that the tweak works.