Clean AC power

You need an occiliscope to see the dirt i.e. what looks like little lines 
going up and down along the AC arc making the sign wave look thick and scribbly because they are very small voltages .
These lines can be in the mega Hz range and down to the hearing range of 20,000 Hz and below and.

I do know that the creator of the dirtiest in-house electricity are motors ,
the refrigerator , the washer and dryer and dirtiest of all the furnace fan moter and the heat pump .  Flourecent lights are a close second .

Most of my AC conditioning is passive , PS audio noise harvesters ,
Greenwave noise filters and everything that is plugged in goes through
a Tripp-lite ultra surge/filter outlet box .

oregonpapa said it best ,
it's noise that you didn't know it's there until it's gone  !

OP conditioners are different from regenerator, and the PPT products Frank mentioned at the top are neither. Using a conditioner or regenerator is compatible with PPT (I use a PS Audio P3 and a PPT gate-“filter”).

I forgot to mention that in addition to everything I listed above, I also use a Sound Application Power Conditioner. I've upgraded the outlets, and pasted the entire inside with PPT's Total Contact. The Total Contact made a very significant improvement to what was already an excellent power conditioner. 

Here’s a review:

http://www.soundstagenetwork.com/revequip/soundapplication_xe12s.htm

Frank

I use two Chang Lightspeed CLS 709 power line filters.

One on main stereo system, and one on home theater system.

As mentioned, your system may sound noise free, until you add a noise reduction device, and notice a big change....more 3D soundstage, very quiet background, clearer, brighter video, etc.

@nonoise,

Thanks. The improvements you report are just what I'm wishing for. Was hesitating on regenerators, with PS Audio's entry-level being double the price of the Audioquest. Believe I will start just where you did and, with luck, maybe need look no further.