Isolation transformer question

I found just messing around that feeding the ESL bias supplies from the lowest power PS Audio regenerator does make a small improvement in sonics. Years ago I tried 6 different power cords on my then SL M1 speakers (before I bought the present PX845s), and I heard differences with SQ having no relation to the cost of the power cords. In fact, the OEM SL power cords (basically 14ga hardware store types) were 2nd best of the 6. Go figure. Any noise inherent to the bias supplies can potentially move the diaphragms, much as spurious motion of a cantilever can also cause distortion.

There’s no attempt in this discussion to distinguish among isolation transformers vs isolation transformers plus regulation and/or additional filtering using caps and inductors vs just a box of HD caps and inductors that filter only vs AC regenerators, which are actually amplifiers designed to take in wall AC, convert it to DC, then output it as 60 Hz at 120V (or variants thereof). These are 4 kinds of very different devices. 
 

I use an AC regenerator on my basement Beveridge speaker system because the AC down there is contaminated by utilities, and it’s made a difference. On my Sound Lab system I use a small PS Audio regenerator just to feed the ESL bias supplies. That was a serendipitous discovery. Anyone who thinks the linear PSs built into our gear are universally well designed and deliver perfect DC ought to invest in an oscilloscope.