Hi ms: For some strange reason, some company's (including Bryston, Canada) eschewed power 'conditioner's' (for decades) to be used with their power amps -yet refused to elaborate.
But today (and over the past ten years I'd guess) Bryston not only recommends Isolation Transformer conditioner's, but has an entire line of them -with their name slapped on the chassis.
The reason is clear; lower, and lower AC line impedance is very desirable for equipment, particularly p-amps. Keep in mind, Bryston's "conditioner's" are simple Isolation Transformers -NOT operated/designed for Balanced/Symmetrical operation.
( The USA's EQui=tech appear the only (strong) Balanced/Symmetrical AC Power supply's.)
I wish I had more experience with today's digital hi-fi used with today's AC-Regen's, but by reading more up-to-date reviews tells me the astounding improvement with digital powered by a quality AC-Regen., remains the same today - a considerable, remarkable enhancement to SQ.
In any case, when you state: " ....But perhaps if our mains has some specific distortions ...".
Let's be clear; we ALL have a bewildering array of AC-line distortions -if being powered by the 'Grid'.
To believe otherwise, is unwise.
pj