What was the first power cable that you noticed a difference in the sound?

@curiousjim I can think of only 3 possibilities.  

1.  your amp has a power supply that stores power for dynamics and bass in capacitors, chokes or other passive devices so tthat a large power cord isn't needed.  this is most likely.

2.  you're listening isn't good.  Not likely.  You're a veteran.

3.  your system sucks so bad it doesn't help  also extremely unlikely.

If you have a power problem with your amp, it will be immediately obvious when you install a $30 10awg power cable from ebay.

Now other components, such as DACs and streamers, have such minor power needs that it isn't unusual for a power cord upgrade not to change anything.

Jerry

@bigtwin Yes, that is my thought.   I have a friend who rebuilt his tube amp to sits on top of a bank of capacitors twice the size of the amp.  All the power cable has to do is keep the capacitors charged up. this is a very flat power demand.  

Cable deniers usually base their claims on their superficial understanding of electricity.  If you amp's average wattage is 240 watts, then you only need 2 amps and an 18 gauge cable is plenty big so 16 awg is "oversized".  What they miss is the extreme dynamics of the load in an amp where 50 amps might be needed for a picosecond.  

So if you have power available downstream of the power cable that can respond to these dynamic demands,  then the amp will be insensitive to power cables.  The cable only has to provide the nameplate wattage of the amp, which is relatively low. 

OTOH, I have a tiny little tube amp, a Sophia Baby, that weights 13 lbs.  I thought surely a 14 awg cable would be plenty for it.  after a couple of days of disappointing bass a friend suggested a bigger cable and immediate improvement.  In retrospect, it makes sense since this small amp has a minimal power supply.

Notice that I have ignored all the magic dust in $4000 cables.  All I have addressed is cable size.

Jerry