Do power supply units/cables make a difference in sound quality?

My two cents, both as a designer and a listener:

AC cables - no difference unless there is a serious problem with one.

Line (noise) filters, from LC filters to isolation transformers to regenerators do in fact have an effect.  Blocking noise from digital components that may be part of your system is also valuable - meaning put the computer/server/streamer on the DIRTY side....

yes a good internal power supply will minimize much of this, but ground noise in particular does come through, albeit at a very low level.

I also ensure that the wiring is up to snuff ( i have a 20A home run from my service panel) and the outlets are good quality ( i use the highest grade that Home Depot sells). A quick look at the construction shows how chintzy the cheap outlets are.

A cheapish experiment might be just losing the outlet strip and installing a quad on the wall.  Surge protected outlet strips in my system did not help, and outlets are relatively cheap to install.

quick comment on some above.  Surge suppression and noise filtering are (almost) totally different beasts. A surge suppressor will have essentially zero sonic impact.  A properly designed filter however, will take noise well above 60 Hz out of the AC signal.

Don't confuse the two.