Brian-Gaff wrote

I doubt one could retro fit anything to anything to cope with this. the
components need to be in the power supplies

To get the best result anyway.

and in some cases the design is so bad that the little transformer
saturates and makes things much worse as everything has sharp edges and
lots of harmonics.

The obvious thing to do is replace the wall wart with one
of the older linear ones with an iron cored transformer.

You could also replace it with a better designed switcher but
it would be rather harder to work out which is better designed
particularly when buying them on ebay or amazon etc.

The dvd is a cheap Panasonic, but it sounds very good, though I've not
managed to work out how to play a cd yet without it muting between tracks
as if you had select the tracks manually, not just let it play the whole
cd. Annoying on some classical sound effect and segway type material.

The original question might be rather academic if
you decide that that behaviour is not acceptable and
return it for a full refund under the sale of goods act.

the True call looks like a coommon Chinese type wall wart to me.

Yeah, haven't noticed many of those brands that put too much
effort into the design of the wall wart now except Apple and
I haven't checked the Apple ones for interference either but
it should be easy to borrow and Apple one to try. Hardly
any normal wall warts tho, they don’t even bother to
supply a car charger for their phones and ipads.

alan_m wrote
Brian-Gaff wrote

Two devices bought this week. Both work OK but the problem is that their
power supplies being of the switch mode kind push out lots of annoying
RF at frequencies between 100khz and around 20mhz.

You need the Aulterra Whole House Neutralizer as mentioned in one of the
recent Russ Andrews threads