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. 

tvrgeek

Now, do these have any effect on the sound? No. None. Time after time this has been tested objectively ... It is a shame that some companies who do make true top notch amplifiers sell such total snake oil.

You can now profit from snake oil while serving your fellow audiophiles.

You Can Get Rich From ’Snake Oil’!

You’ve made the claim of snake oil here, now please take it to the next level. Take ’em to court. After all, "Time after time this has been tested objectively." You can’t possibly lose!

This youtuber uses a gizmo to test noise on the AC line and compares it to Furman and AQ Niagara. 

In my system, I recently traded out an AudioQuest PowerQuest3 for a Niagara 5000 w Tornado power cable. The sonic result was a substantial increase in realism, among other things. I expected to be disappointed with the results from the trial, thinking the cost of the Niagara couldn't warrant the price tag. I don't want to remove the Niagara from my system now. 

Interestingly, guys over on WhatsBestForm say that running two Niagara 5000 is better than one 7000. One dealer I know also runs two Niagara. 

In my TV space, I run a Furman PST-8D. Now that I have a freed up PQ3, I'll compare them to see if I can see or hear a difference. 

@oddiofyl - The rectification happens on the secondary of the transformer. Meaning it doesn’t "know" that the primary is balanced or not. It’s perfectly safe to use with tube gear.

Please keep in mind that whole-house surge protectors have high clamping voltages compared to the best point-of-use surge protection. About 600V vs. 200V. Whole-house suppressors are not intended to be the only surge protector in your home, especially for delicate electronics.  I've lost a laptop that way.

Having said that, tube gear by nature of the higher working voltages may be less susceptible to your average surge.

@erik_squires What Furman gear models do you use for voltage regulation and surge protection?

Many manufacturers ask not to stack surge protectors with their uninterruptible power supplies, but those UPS's are some of the only gear I've seen that will control voltage (or at least measure voltage).