Small correction, you mean Tim at Blue Dog!
As Pucho 812 corectly comments a modern switching module itself isn't a problem for a 'raw' DC BUT noise in the form of hetrodyne whistles in the audio range CAN be an issue. Whether it is a problem for any specific piece of gear will depend on many factors such as the internal wiring layout inside the gear, whether it has some filtering that is still working (not aging electrolytics) and where 'noises' may cross into audio paths. The issue was discussed in 'Studio Sound' magazine about 30 years ago when a hire company using several desks previously using linear supplies plugged in a 'new' switcher and discovered increased HF distortion on audio outputs. As that particular desk design had provisions for 'hot standby connection of supplies tests were carried out by comparing the situation when the desks were running oNLY on the linear and then by powering up the switcher (no break) then turning OFF the linear the change in performance was measured. By strange coincidence I actually worked with the engineer (specialist) who created a suitable filter network to remedy the issue.
Using latest 'switchers' that have Power Factor Correction is GOOD for power wastage BUT the 'noise' on their outputs is a complicated cacophony as PFC operation is effectively a switcher running directly into the main switcher and you have to consider filtering of all connections into and out of the switcher module. Something RF designers have been doing for many years of course but in the context of preventing RF oscillators 'leaking' into sensitive bits of circuitry. I talk with Tim (Blue Dog) regularly and have one of his units in my 'kennel'.
