Power Conditioning on the Cheap

FWIW, I’ve tried and researched a number of solutions... even opening them up (or looking at photos of various internals) to see what they’re made of. I don’t have any insane demands from a home theater perspective, Marantz pre-pro, Rotel amp, phono stage, turntable, BD player, sub, and Martin Logans. The APC H10 (which I have used with past incarnations of my home theater) has been an absolute champ. For a shade over $200, it’s feels like an absolute steal. I’ve cracked open alternatives in a similar (and sometimes considerably higher) price range and laughed at the wool companies like Furman are pulling over people’s eyes thanks in part to the fancy chassis and LED displays. One Furman unit I bought (and subsequently returned) was costlier than this particular APC and the chassis was barren and the contents looked like little more than a budget surge strip inside. The H10 may not be much of a looker on the outside, but it’s got it where it counts. https://www.apc.com/shop/us/en/products/APC-AV-1kVA-H-Type-Power-Conditioner-120V/P-H10

Furman makes a lot of units at different price points. The key features that step them up from just a couple of MOV’s in a box:

• LiFT
• SMP

If they don't have this you are right, they are really basic.

I’ll add APC (H15) to your list for consideration.
 

I got mine used. It’s a long story, suffices to say it save my previous pre/pro at a rental w/“ISSUEs” even a dedicated 20A wasn’t enough.  

On the cheap you can get a nice Topaz, Xentek, ECA, MGE, Daitron, Elgar, etc. extreme/ultra isolation transformer, then just pop a nice passive power strip or two into the duplex. You can get a 0.005 pF 120v 1 KvA Topaz model on eBay fright now for a little over $200, but it needs a good cleaning (I'd use 91% or higher isopropyl alcohol or De-Oxit), which may mean a new duplex as cleaning in there can be a son of a gun. Just something extra to consider.

These Ultra/Extreme isolation transformers massively reduce noise, more than power conditioners and regenerators and such that cost over $10,000. There's a large thread about them on HeadFi, and the original poster measured common mode noise attenuation of over 150 dB at a pretty wide frequency range (up to roughly 9 kHz, 140 dB up to over 1MHz and transverse/normal mode mode attenuation of up to 65 dB) on a common model (not even one of the super low pF models).

Make sure you get one with voltage in and out that's compatible with your house and equipment (120v, 240v or one that can do both). I accidentally bought one about 6 years ago that didn't have the voltages listed and in my then naivete tried to make it work but it was 240-250v only.

These units weigh 40-60 pounds though and are shielded like a tank, so be careful.

From what I can recall Xentek and Elgar have models with the lowest listed capacitance out of all of them (0.00001 pF models exist), but they are super rare to see. Topaz has some slightly more common models at 0.0005 pF. ECA doesn't list their capacitance, but it's under the Extreme nomenclature that Xentek uses (most of these transformers use the Ultra naming). The nice thing about ECA's is that is comes (at least my two have) with balanced wiring on the output duplex and has a capacitor wired into the duplex as well (the capacitor on the transformer that I added a new outlet to was a 7uF 250v 50-60Hz polypropelyene film capacitor from Aerovox). I actually want to see if I could add an even nicer capacitor to it but my capacitor knowlege is limited so I don't know what to replace it with aside from one with the same rating and 7uF capacitors are rare today.

While I value power conditioners for surge protection and lightning protection including such lightning protection for FM and TV antennas (to which I add lightning arresters where the cable enters the house) I am skeptical of their ability to do anything the amplifier and preamplifier ripple filters do not do better. With a good ripple filter such as a pi network with an indictor the components filter full wave rectified 60 Hz (typically by two diodes, sometimes vacuum tube, and a center-tap transformer winding output). Double that frequency and they are twice as effective because capacative reactance is inversely proportional to frequency and inductive reactance is proportional to frequency. At frequencies higher than auditable, say, 20 kHz, this factor is 500/6 for a reduced fraction of 20,000/120, the fundamental frequency of a Fourier series of full wave rectified 60 Hz. I admit at radio frequencies capacitance between inductor windings begin to occur, but vacuum tubes used in audio are not likely to amplify these frequencies. The 833A which a very few people use for the final stage of their SET has a cutoff frequency of 20 mHz and other audio tubes are likely to be similar because they are not designed for VHF. And if RF passes through the inductor in the power supply ripple filter, it is certain to be shorted out in the output transformer windings of the amplifier. 

Therefore I am not surprised if you hear no change from an expensive power conditioner. Still, I see no harm if they do not add to the price and if they add shorting effect to unusually high voltage spikes.