Power Cables and Wall Sockets

A 15 amp circuit usually only has 14 gauge wire in the wall.  However, this wire is generally solid copper and of good quality (not audiophile copper, but of good current capacity).  Most IEC cords are smaller than 14 ga.  Even a 14 ga cord adds several more feet of losses.  Something non-intuitive is that losses are additive.  If you have 100' of 14 ga wire and 100' of 12 gauge wire, it doesn't matter what order they are in, the current delivered to the component is approximately the same so putting a 10 ga power cord downstream of 14 ga wire does make sense. 

And finally, the answer to your first question is yes.  Many of us upgrade the power circuit to our audio system. I have a 10 ga circuit run from the breaker box to my system.  

Jerry

If you amp is causing lights to dim you have an extreme power problem.  If the lights are dimming significantly, the circuit is overloaded, the breaker should be tripping.  The circuit is overloaded.  There is an increased fire risk.  Jerry

@imaninatural   I know how important it is not to appear to bash expensive equipment, but I do not recommend expensive power cables.  I recommend heavy gauge power cables.  I use 10 awg for all my amplifiers.  I've never spent over $100 on a power cable.  YMMV.

@builder3 rereading your post I'm not sure we disagree.  All the homes I've seen in CA have 14 gauge wire for 15 amp outlets.  I just installed a new circuit for my stereo using 10 awg. The old one was 14 ga/15a.  I've never come across a 12 gauge wire for 15 amp service but you can do it.  In my home, all the 12 gauge circuits have a 20 amp breaker.  I know because I replaced my breaker panel and breakers.  --Jerry