Are manufacturer AC cables good enough?

How good are the power wires running behind the walls to your power sockets?
I don't think it would make sense to buy expensive power cables if the wires supplying power to your sockets are of regular quality.

I did try and I did hear...and not subtly.

If you did not try in a blind controlled test then you're just offering subjective biased opinion.We ALL have subjective biased opinions when it comes to seeing and hearing the only way to know if something actually works is to remove the biases as much as possible. One of the best examples of conducting an ABX test is done by Floyd Toole when he was at Harman. It's controlled by computer and the results from blind compared to sighted is very revealing. It's and hour long if you care to watch it. 
https://youtu.be/zrpUDuUtxPM

I run a Lindemann, PMC, JL Audio system. Recently upgraded all my power cables to AQ and NRG. Was anticipating a big audio improvement. There was a slight improvement I believe when I switched back and forth between the stock and after market power cables. Not the "Massive improvement" toted by the cable manufacturers and testers of those products. Although there is a huge difference in the quality of the cables look and build. The NRG cable is truly a work of art so I am happy. 

Power cord must be:

1.UL rated
2.Originally supplied, or meeting same specs as original
3.Long enough to reach your units easily ie. no tension
4.Connected to a good quality surge protector (unless your stereo is a cheaper crap than the power cord itself ;) )

Did I miss something?...pls add

"subjective measurements "
??

this is an oxymoron term....

same as 'anti-aging' face cream....