Power Conditioner Architecture. Discuss Differences?

PS - The latest PS Audio's limits are known, like you say they are essentially amplifiers, but the noise on the output is unexpectedly high, even given Class D.  Modern audio Class D amps are much better when driving sppeakers.

Perhaps a future version of PS Audio's regenerators will use spread-spectrum Class D to minimize that. 

Personally I'd rather use mechanically switched voltage regulators.  Even more efficient, no amplifier switching noise and all the current my wall can provide.  The one negative is the mechanical noises.  The switching as well as the occasional mechanical hum. 

This brand/unit is AFAIK out of business and never got the right kind of distribution but IMHO had the best mix of design and features.

Instead of either a linear or switching amp to regenerate power (i.e. PS Audio) ExactPower used a buck/boost transformer to actively fix the incoming AC signal from moment to moment. The advantages were many, including extremely high efficiency (comparable to latest gen PS Audio) and very low noise (unlike PS Audio now), and excellent fine-grained voltage regulation.

The one feature it did not have was the ability to arbitrarily change the AC frequency. which is fine by me since that’s extremely tightly regulated already.

Sad to see it wasn’t more accepted in the market.

https://hometheaterreview.com/exact-power-ep15a-av-power-regeneration-device/

You missed inductive and switched regulators.

Series mode surge protectors fit the former.  Besides the actual surge suppression the benefits are very low start to filter frequency, around 3 to 10 kHz.