I heard the sonic imbalance (an unpleasant leaning towards the higher spectrum) and thought it was the speakers, the amp, whatever. Some weeks later a friend came over to test for distortion on my dedicated power line and we found that some had remained. Most tellingly there were periodic spikes that my friend said were typical of phase cutting and asked me if I had a switching supply somewhere. I pointed to my Cambridge DAC, and pulling the plug, the spikes were gone. I bought a linear power supply instead. The sonic imbalance was gone. Not sure if it was the switching itself or that the new power supply is simply stronger.
The (a) problem is determining the real root-cause is in your particular case. The SMPS could be the source of the noise (or not), but the cause of audible degradation could be ground leakage, EMI/RFI (radiated noise the component is unable to reject), leakage through the power supply, etc. Including perception bias leading to hearing things that are not there -- that happens way more frequently than most of us realize. I learned that lesson the hard way several decades ago when all the grains of sand I heard in cables and such, were totally unhearable in blind tests, even when I
knew what to listen for and was
certain it was there.
From the wall the voltage is converted to DC and regulated so isolation from the wall to the audio signal is extremely high. And the noise from the switching supply is much (several decades, factors of ten) higher than the audio band so it could not be the source of the noise directly. It could be interacting with one of the components to change the sound due to poor noise rejection.
Explaining digital signal processing is beyond the scope of a simple forum post; it takes research. Note your components are performing analog signal processing, and DSP has largely replaced ASP in part due to those very concerns you expressed: ASP introduces phase changes, amplitude variations, higher sensitivity to component (processing) and environmental (e.g. temperature, supply voltage, noise) variations, and so forth. DSP can perform signal processing (which is much more than simple filters, for ASP or DSP) much more precisely, with greater stability, and over a much greater range of parameters and such without corrupting the signal. DSP is used to correct amplitude and phase problems due to other components in the chain, including the speakers (typically the greatest contributors to frequency amplitude and phase issues).
IME too many folk, in many fields, reject out of hand things they do not understand. And the worst are those who have a very limited and quite wrong understanding, often driven by marketing, and refuse to perform enough research to determine fact from fiction. They've already made up their minds and arguing is a waste of time for all parties. This happens in all fields, not just audio, natch. And the one certainty I have is that I am not immune to it.
I offer this anecdotal audio exchange:
https://www.audiosciencereview.com/...all-the-wrong-things.9588/page-12#post-256109
FWIWFM - Don