Power Conditioners

Here’s what I assume:

• Surge protection/protecting gear is a must.
• Some (modest) amount of power treatment is at least warranted as an experiment, just to pay respect to the quality of gear one has invested in.

The questions get trickier when one asks:
(a) how much investment is worth the $$ and
(b) which kinds of treatment and how much should one spend.

I suppose the trickier questions can be tackled by doing comparative listening (with various power gear) but BEFORE one goes and tries all that it would help to narrow down *what* to compare.

So, here are my questions: 

• How might one measure the quality of power on their line prior to listening?
• What tool would one use? 
• What measurements strongly correlate with audible effects that detract from the music?

I purchased the Audioquest Powerquest 2 at my dealer's recommendation. I was returning a $1,000+ power conditioner I had been demoing and decided against buying. 
I was thinking there was no way in the world a $199 unit would work. But it did. There was a significant improvement in the sound.
I would suspect the results differ based on how revealing your system is.
But, I immediately recommended it to several friends.
Order one from Amazon and you can return it if you'd don't hear a difference.

Having lived in large cities through out most of my life I’ve noticed a large change with noisy AC having moved to a small community.

I’ve spent lots of money over the decades on conditioning , regeneration and what have you and was never content for long always looking to tweek and upgrade something.
Currently we live in a small community and I’m much more content with my system then I can ever remember though I use Synergistic conditioner and Ac cords through out a further drop in the noise floor was immediately noticed something that wasn’t so evident living in a city .

ecrotty if you live in a large city try out regenerator and transformer base conditioner if you can. 

Even expensive Power conditioners did not make sound better.  Actually my Pass Labs mono blocks  did not like them. 

I'm rural, and my area is subjected to power spikes, dips and outages.  Some years ago I bought a Belkin PF60 (https://forum.audiogon.com/discussions/review-belkin-pure-av-silver-series-pf-60-ac-filter) for the surge protection, not any power "conditioning" designed to make my system sound better. 

After some time, I noticed I was getting a very faint, low-level hum/buzz at system idle with no audio or video signal passing through the system, and eventually figured out that my cable box hadn't been routed through the Belkin's "Cable TV In/Out" connections (my system doubles as HT/2-channel).  It was just HDMI-connected to the A/V receiver.  Re-routing through the Belkin eliminated the background buzz without any noticeable change to any video/audio signals.
FWIW