However I am conscious that
in a quiet analogue environment, the SMPS may be a problem with
switching noise. Is this a feasible idea?

Richard-

This will probably be a good learning experience for you.

I purchased the Radio Shack switch-mode power supply, and was not surprised
when it caused severe interference with my receiver. Then I bought an MFJ 25
ampere supply that had a good reputation, but it also caused i some
interference.

When I bought a new Icom rig, it came with their switching supply. Although it
is the quietest of the three, there is also an increase in the noise floor when
it is in use.

To be fair, I must mention that I'm using a magnet-mount antenna on a nearby
clothes dryer. An outdoor antenna would certainly receive less radiation from
the power supply. At least you see how easy it is to pick up the switching
noise, and how hard it may be to eliminate it!

73, Fred, K4DII