Who Tried Power Conditioners Over The Years and No Longer Use Them Today, Any Why?

Depends on your system and its resolution I love mine VIBEX Platinum 2 units.

I’ve used a variety over the years, both conditioners and regenerators. Let’s see: TAD/Bybee; Bybee/Curl Pro; PurePower 2000; Running Springs Dmitri; Audience’s top duplex wall mount, whatever it was labeled, just for my phono stage. Once I installed 4 20-amp dedicated lines with top Furutech duplexes and a separate subpanel running directly back to my new 200-amp service, though, I pretty much gave up on conditioning, etc. I liked direct to the wall better. Then I tried AudioQuest Niagara 5000 around 18 months ago, just to see, and it has stayed in my system ever since. With everything in the signal chain plugged into it (very important to cut ground noise), including high power class A amps (when I use them), the noise floor drops dramatically and everything is at once more detailed and more natural. AQ Hurricane cords all around really help, too. Now 3 dedicated lines sit unused.

When my PS Audio  AC Junction box overheated and bit the dust, I replaced it with a generic TripLite box that happened to be in the house. Son of a gun, the stereo sounded better with the TripLite. I still though, connect the TripLite to my groovy PS audio wall outlets with the hefty PS Audio AC cord that came with the PS Audio box. Agreed, I was never able to do  back-and-forth comparisons, but I just don't care enough to fret over it. I'm getting good sound, and that's enough.

As @ebm said it will depend how resolving your system is.

I have dedicated 200 amp service and I am isolated from the rest of the house. Only my system is on this circuit. I also have Signal Cable power cords and interconnects on my system.
In the past I had several different power conditioners on my system and now I have my AH X200 direct to Hubbell IG5362 Duplex Receptacle and my other components pulling power from a Furman SS-6B-PRO with the NFC Line Conditioner. Thinking of upgrading the Furman looking at the iFi or AQ1200 Will buy where I will have return privileges..

Will buy where I will have return privileges.

@jerryg123 , that's what I did with the AQ5000 and it stayed.