Some power products perform a function, some do not. :(
A very good surge suppressor: fast diode, spark gap, etc. does in fact help protect your equipment. I suggest a whole house suppressor at the panel as well. Look at the response time. Many out there just toss in a 50 cent MOV with slow response and no filtering. I kind of like Trip-Lite products but there are many others. FWIW, I recently had my PC blow up from a proximity hit and it was plugged into a Monster strip. I can't actually blame it, but don't trust it either.
A suppressor/RF filter may reduce noise injected through the power supply IF the supply is garbage and system grounding was not well thought out. Any quality product should be designed to work on lines power and assume it is noisy. Most mass produced stuff is, ironically some of the most expensive prestige stuff is the worst at this in the marketing "purity" game. Some is really great.
A DC blocker ( I have an Emotivia) will eliminate issues caused by DC on the line. I had issues with toroid transformer vibration on and off from dimmers and LED ballasts.
I run a Pyle sequencer on my main stereo so the PC music server via USB brings everything up and down in a reasonable sequence. I used to have an active crossover that would cause a killer thump, so with this I could power it on first and kill it last. Everything was fine until a power hit took it all down. The thump almost knocked me over! Furman makes similar products. They are de-facto in the PA world. When I ran 3 Parasound 1200's, I had to have one as the inrush from all of them at once would drop the 20A breaker on my dedicated 10ga circuit.
Now, do these have any effect on the sound? No. None. Time after time this has been tested objectively. You could run a square wave old school UPS into your stereo and not hear the difference. I did once. It is a shame that some companies who do make true top notch amplifiers sell such total snake oil. Of course, I do not discount the ego/placebo effect. If you think it sounds better, then your enjoyment is the goal.
Lines power is designed for ight bulbs and motors. No other guarantee. Not distortion, noise, voltage, or frequency. It is the responsibility of a consumer device to deal with that. A big old IE core transformer does a superb job. So do switchers but they carry their own issues.