Are manufacturer AC cables good enough?

Thanks I watched Mr Winer's You Tube video.  Smart guy.
I had a friend over who believed all in science, being that upgraded interconnects do not matter.  He wanted to try his DAC in my system, so we inserted it with his balanced interconnects.  It sounded poorly compared to my DAC (to the two of us).  Then I re-connected his DAC with my Audience AU 24 SX cables.  Wow.  It sounded better (to our ears). Easily.  We switched back and forth.  He was dumfounded that the interconnects made such a difference, as 'science does not support it".
So, if it sounds better (in all the subjective ways) go for it and enjoy!  If you do not believe, that is your opinion, or your science!  Isn't subjective pleasure the basis of our hobby?  

I bought my first aftermarket power cords after getting a PS Audio power plant, the Stellar PP3. First, the cord the PP came with is pretty darn stout. I replaced it with AQ’s NRG4. I got two Shunyata Venom 14s for my Rogue Sphinx amp and DirectStream DAC (Magnepan .7 speakers). I have moved them around and don’t hear much difference between cables, but overall the system has what I’m going to call greater articulation. It’s just clearer sound. I’ve never used the $$$ cables so can’t say. But I suspect the “diminishing return” curve kicks in really, really early once a good conductor, insulator and connector are used. But I guess that depends on your definition of good.

Can someone please help me through the following line of reasoning:
AC current travels 2-3 miles from a transfer station at 220 volts, enters my home into a distribution/circuit breaker box, travels through 45 feet of 12 gauge solid copper wire at 110 volts to a plug in my wall, into which I place a 3-foot long power cord.....
How can this 3 feet of power cord transform the electrons that have come so far into some magical source of electricity for my components?   It does not take much metal-to-metal connectivity to provide 100, 200, or 300 volts into a device.....

jbmays:  Hearing is my reasoning!  That is the only reason I upgraded my power cables.  Do you get that?  You don't have to understand it to appreciate it.  That is what everyone is saying.  If you don't get it (hear it) then you don't need it. 

jbmays

Can someone please help me through the following line of reasoning:
AC current travels 2-3 miles from a transfer station at 220 volts ...

No, that's not at all how power is distributed, but at voltages that measure in the many kVs, probably 4,800 kV minimum.