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

You have a very fine system! Don't fall for the malarkey that special power cables and AC conditioners are a necessary part of a quality system. A system's sound starts with the power supply of the various components. NOT with the wire from the AC outlets! RF noise from the AC outlets is a non-issue for any competently designed power supply. I always leave the components' captive power cords alone. I don't use power conditioners/AC regenerators. These are just to get the gullible to spend more money! 

Ever since Noel Lee brought forth his Monster Cable company around 1976 the audio scene has been plagued by hyperbolic ad copy extolling the virtues and superiority of Cable A over Cable B. Before that audiophiles used zip cord and Radio Shack gray Switchcraft interconnects - and nobody complained! Suddenly manufacturers saw great profits to be made selling "audiophile grade" wire to the masses. All the claims of the superiority  of one cable over another have ZERO bases in scientific evidence. "My golden ears tell me it is so" is the common refrain! Like the eyes being fooled by optical illusions human ears and hearing are easily fooled!

Those that claim to hear a "sound" from different power cords are in the throes of confirmation bias. Naturally the shiny new toy always provides more enjoyment - until the thrill wears off!