PS Audio Power Plant Premier AC Power Regenerator/Conditioner.
One owner, works perfectly. I bought this originally to protect super expensive single ended triode gear from spikes and other junk on the grid. It completely regenerates the AC so there's no way anything untoward gets through.
Later I used it with conventional gear and found it lowered the noise floor of the system and made other impressive improvements, so I kept it.
I ran 75 watt/ch power amp through it, worked fine, no softening.
Very clean. Conservatively graded.