There are plenty of articles that show measurement of these kind of applications. First of all the mains power is converted to DC in all Amplifier circuits with rectifiers and capacitors sequences ... and it is therefore impossible to occur, yes: it is strange & asburd to think that any noise will make it into the DC supply. There are measurements done on audio equipment without or without a noise main power ... and ... it ... does ... not ... make ... a .... difference. Why does WH not do proper technical reviews instead of saying things like "no harm in trying one out" for £1000-£2000 per piece? Why does WH not proof if this piece of equipment does what it claims? Why does WH not protect the consumer instead of screwing them over?
Realise this post was from several months ago, and I agree that some mains blocks or filters may be examples of ‘snake oil’ or ‘gilding the Lily’, offering only minimal improvement, if any.
But, having lived close to commercial & industrial estates & near a Network Rail substation, I can attest to the value of dedicated mains regeneration.
And even more expensive the installation of Hi-Fi dedicated MCB/RCD feeding into Twin & Earth ring-mains & switchless sockets fitted with high grade fuses.
While their effect may have been fairly incremental on some components, the improvements ie. blacker background/lower noise floor, more articulate & coherent bass, opened up treble frequencies, soundstage dimensions etc. i’d say were more noticeable & probably more worthwhile for sensitive source electronics(ADC’s/DAC’s, CD/SACD players/transports, servers & streamers) & were audible to my ears as well as those of my friends - only some of whom could loosely be described as Hi-Fi enthusiasts.
After consulting a couple of electrician friends - who have their own modest home audio & home theatre systems - even they were somewhat at a loss to explain the improvements they’d heard.
Almost all of the components were well used ex-dem/pre-owned. Not for crazy money initially either. It’s possible that with time the internal components were showing signs of their age & beginning to deteriorate.
Anyway. Who knows how or why it sounded ‘better’?
It’s all about the music(or movies) at the end of the day.
All the best.