1 - There are EMI/RFI filters, and wave shaping filters. The first aren’t doing anything below 100 kHz and are in parallel, the latter aren’t doing anything below 3 kHz, which is well above the 50 or 60Hz line frequency. I really don’t understand why people think that the power pole is cleaner than the power they have at their outlet, it often is not. The last thing I want is a super conductor between my amp and the power pole, which is what seems to be the target for audiophiles. I want resistance. I want inductance. Enough at least to reduce noise transmission and ensure surge protectors have time to work.
In order of preference, Furman and Tripp Lite, but please do take a look at the Wirecutter article as the brand AND model matters. Furman without SMP/LiFT is just another power strip.
2 - Well, the type matters because it’s not always on. I use these strictly for my PC, Internet access devices and CPAP. The PS Audio units are essentially the same idea, with Class D outputs (and noise) and very short run time. 🤣 There are UPS with sine wave outputs which are still a lot cheaper than the PS Audio units, but for whatever reason, the sine wave units tend to have a higher failure rate than the stepped voltage output units.