What is a power regenerator?
Regenerators are conceptually very similar to online UPS systems except that there is no battery. They are basically amplifiers designed to output 120V at 60Hz . Done right, with a low distortion sine wave inverter, power regenerators offer protection for all power quality issues except interruptions and the high degree of isolation between input and output significantly reduces powerline noise.
Whilst the technology seems perfect on the surface there are a couple of real life issues:
Limited maximum power.
PS Audio's flagship P10, for example, can only provide 10A continuous, which might not be enough for large home theaters with projectors.
Limited dynamic power.
That same P10 has a dynamic current rating of only 12.5A, which is much much less than the wall as well as that offered by isolation transformers.
Failure rates can be high. As an active technology there is more to go wrong than with a passive unit. There have been reports of near 10% annual failure rate with PS Audio's previous generation units.