"Ian Bell" wrote

I should also have said that my experience with linear supplies is that
there is a huge amount of crap on the mains from laptop SMPSUs and the
like that falls squarely in the audio band. RFI filters are not effective
in the audio band of course.


I agree that there's plenty of audio-band crap on the mains, but not from
SMPSs, which generally work at frequencies well above the audio band. AF
crap is either harmonic distortion of the mains waveform, or comes from
commutator motors and the like.

AF crap shouldn't be a problem with a linear PSU. The transformer will
remove common-mode noise, whilst the filtering on the rectified output
(which you need anyway to remove mains-frequency ripple) will eliminate the
rest.

David.