I’ll second @adasdad’s opinion that the Niagara line is worthwhile. Since I’ve been in this hobby, I’ve tried the Furman PST-8D, AQ Powerquest 3, and consumer-grade options by Tripp Lite and CyberPower. None of those units made much of a difference for me. It wasn’t until I picked up a Niagara 1200 and 5000 that I heard positive differences. I was skeptical that the 5000 was going to be worth the cost, but it made such a big difference that I consider it an essential piece in a hifi rig now.
I don’t know the guy, but there’s this small dealer on YouTube called OCD Mikey. He has said that power conditioners under 1k don’t make a difference. That statement is consistent with my experience. But Mikey is a big fan of Puritan, which is more affordable than most of the AQ Niagara products. I haven’t tried Puritan yet, but it looks like it works well too.
I currently use the 1200 for my TV and the 5000 for my separate stereo system. I don’t feel that power conditioners are sexy, but that they’re foundational. And I feel that I made sonic gains with conditioners I couldn’t have otherwise made.