I don't think that any generally applicable conclusions can be drawn about power regenerators. From both a technical and an anecdotal standpoint their efficacy figures to be dependent upon their own design, the designs of the components they are powering, and the characteristics of the incoming AC.
Obviously regenerated AC that is essentially free of both noise and distortion figures to either be helpful or to not make a perceptible difference, depending unpredictably on the designs of the particular components and on the characteristics of the incoming AC. But whatever limitations a particular regenerator may have in terms of its responsiveness to abrupt changes in demand for current may or may not outweigh that benefit, depending on the designs of the components and the regenerator. And adding to all of that uncertainty is the possibility that the potential downsides of either using a regenerator or not using a regenerator, if present to some degree, may be subjectively preferable to some listeners with some systems.
So it's all essentially unpredictable as I see it.
Regards,
-- Al