In my experience the bad rap for SMPS is that even though a high-speed SMPS is not digital it will induce a bi-directional digital-like noise. Bi-directional implies the digital-like hash / noise travels back up the power cable into the outlet and then induce its digital-like noise into other components sharing the same circuit. Supposedly all digital products induce this bi-directional noise and some say will go all the way back to the service panel and induce its noise across other circuits.
This bi-directional noise can easily be minimized or possibly eliminated with the use of a superior passive, dedicated, bi-directional filtering line conditioner. However, an external bi-directional filtering line conditioner can do nothing to stop the bi-directional noise from being shared between both channels of a Class D stereo amp because the 2 channels' SMPS most always share the same AC inlet in the chassis. And it's far worse in a Class D integrated amp because the active gainstage much borrow its AC power from one of the 2 channels which are already sharing the bi-directional noise. Then the noise from both channels is funneled to the active gainstage and then amplified. This makes for a very unpretty music presentation, especially if the amps are high-powered because the digital-like noise becomes ampified along with the music.
For this reason I only use Class D amps in the monoblock configuration so each monoblock can have its own AC inlet and its own dedicated bi-directional filering line condtioner and hence no sharing of the bi-directional digital-like noise. BTW, superior line conditioners do far more than just filter bi-directional noise. In fact, only a few of the superior line conditioners I'm aware of offer bi-directional noise filtering and since I actually like the performance of some Class D amps and because I use a digital source, my superior line conditioners (Jena Labs Model TWO's) are even more superior since they are also filtering this bi-directional digital-like noise from inducing their distortive harm into other components.