Least Expensive Power Conditioner/Surge Protector That Won't Worsen Sound

I have an old Shunyata Hydra 6 that I'm sending off to Shunyata to repair. In the meantime, I'm curious - What's the least expensive power conditioner/surge protector that won't worsen the sound? 

I've already discovered that plugging my integrated directly into the wall sounds the best. But I have source components. I have liked the Shunyata, but just in case they're not able to get it back to like new shape, what are your thoughts? (I tried numerous PLCs at the time I bought it almost 20 years ago and I thought it, by far, sounded better than any other one I auditioned in my system, and that included the Hydra 8).

I see many users who have reported worsening sound when using the Audioquest PQ2 and PQ3.

Something like a Panamax PM 5300 or 5400?  Or the Furman Elite 15?

And what is the danger of under-voltage?