"I don't know how a switch-mode power supply could provide true isolation without a core
& coil isolating transformer."
IIRC many switching supplies DO use a transformer, often a toroid and coil rather than an old fashioned one. Consider an MPPT
controller. It is a switched-mode supply, but it is applying DC pulses to a toroidal core/coil that is still being an effective isolation transformer. At least, that's the impression I have of them.
With a real transformer, your "isolation" ultimately comes down to just some varnish
on the transformer windings. In a pure switching supply, the silicon junctions in the switches are the isolating element instead. The world has gone to switching supplies for many things, simply because high power transformers are just too damned expensive. (Space, mass, cost.) And too many of them buzz like crazy after they age out.
can be tuned (or detuned) out of the frequencies that would cause RFI problems for any particular user, if the manufacturer provides for that. There are some ham radio
supplies that literally have a frequency offset adjustment for that purpose. Other manufacturers just need to be contacted to ask what their design priorities were, i.e. if they ignore RFI or design for marine SSB