Are manufacturer AC cables good enough?

I make my own from old-fashion style 12/3 round woven fabric cable, hospital grade plugs and lock-in IEC connectors 

kozka,
About 6 hours a day on average (more recently). Also, the earth isn't flat. 

How about Auto manufacturers? I’ve seen some pretty mediocre tires come stock, and on higher end cars better rubber. FWIW, Naim who are fairly conservative. Offer their own upgraded power cables and interconnects, their engineers can hear the difference, so do PS Audio, and I’m sure a few others. Power cords that come with equipment are adequate, and if one thinks that’s all that’s needed then fine be happy, but  don’t Be a Cable Cop !

"Whenever two things are different one is of necessity better, the other worse."

Tell that to people who ask to have half scoop of chocolate and half of vanilla. They may have different view. Of necessity, maybe even better.