THE WALL---Why?

It's a matter of electrons. Specifically, how many electrons can get to your amp when there is a sudden draw. (The wave description is equally valid.) Engineers call this source impedance - ideally, you want a source with zero impedance, like a dedicated power station.

If a dedicated power station is out of your budget, try a large isolation transformer which will clean up the power but not increase the source impedance. Plitron makes a good one - toroidal - good enough for medical equipment - and they sell to the public. Works for me, for all my equipment. YMMD

Should have said that toroids tend to growl when they are doing their job, so it's better to site them in a garage or utility room.

dentdog, I think that 20A should be, how to say it, ample. Doesn’t hurt to over-specify, so long as the equipment doesn’t make an intrusive noise where it shouldn’t.

That’s what I would do.