On Sat, 19 Dec 2020 09:35:28 -0000, Brian Gaff \(Sofa\) wrote:

I already did the ferrite ring trick. Indeed I've never found this
approach to do very much good at all on noisy psus. I think the sheer
wide bandwidth is the issue.

A decent LC filter might do it. Couple of fairly hefty (to handle the
current without too much voltage drop) toridal coils, one in each leg
with 0.1uF capacitors across the in and out. Fitted as close as
possible to the offending wart should at least stop the power lead
radiating crap.

I was even thinking of perhaps getting a couple of those power
bank batteries as when not actually attached to a charger, they would or
should be completely clean

Wouldn't like to bet on it. A Li cell is nominally 3.6V. 5 V power
banks use a DC-DC convertor to step up and regulate that 3.6 V to 5
(+/- 0.25 V).

--
Cheers
Dave.