Power supplies must be considered part of the audio product. While it is easy to think of them just supplying DC volts at an appropriate current, there is as always more to it.
Unfortunately the audiophile community is prone to just throwing overkill current, capacitors and transformer mass at the problem. This can work so they get the impression this is necessary.
First of all SMPS can be fine, but it is more likely to cause issues when not properly matched. The audio circuitry has PSRR: Power Supply Rejection Ratio. This is a measure of how indifferent an audio section is to noise on the power supply. This should be hugely indifferent, at low frequencies where "linear" supplies opperate. However SMPS are high frequency, where the rejection needs to be considered. Some sections, even opamps, have gain from the power suply, not rejection. So a badly matched supply can add noise to the output. Rare to measure it directly in audio magazine style measurements, as it hides in less conventional measurements, but not to be ignored.
I take exception to the term "linear" power supplies. They are usually very non linear when it comes to power amp supplies. But they are easire to cope with.
A good SMPS is very likely to be better than linear, but only with understanding and system wide design, and not some throw in wallwart.
