Testing for Dirty Electrical Power

Please see this article at inCompliance Magazine for EMC professionals: 

It is good to avoid "instant reward" measurements that produce results that mean very little.  For example, converting EMI into audio signal would work only if the high-frequency signal has modulation within audible range.  Very short spikes (microsecond-long) may or may not get converted into audio.
Make sure that you have valid numeric results - not some ambiguous relative numbers, but absolute values in mV or dBuV.  If you are committed to accuracy and relevancy of measurements, it would make sense to invest into professional tools.  There are plenty of inexpensive oscilloscopes on the market with FFT which allow you measurements of both time-domain signals and spectrum as well. I use Migsig oscilloscope STO1000 series (https://www.micsig.com/product5/)  Hantek has reasonable oscilloscopes as well. 

To connect oscilloscope to live power and not blow your oscilloscope's input use EMI Adapter: 

There is a whole field in the industry on both measurements of EMI and its mitigation with the tools and methodology that is yet to filter to audio applications...

For me the best solution was to go with power regeneration.  Nothing like having a very clean AC going to your equipment.   It is like upgrading the power supply on all your components.  

Seems like the best audiophile power solution is to run on battery like the Stromtank. Unfortunately it’s currently out of my budget and I don’t have room. 
Power regeneration garnered mixed reviews, especially with PS Audio products.  
I followed MikeL balanced power suggestion and use an Equi-Tech.  Equi=Core also gets good reviews 

I agree with bmontani's comment on regeneration.  Someone whose opinion I have great respect for suggested this.  I bought a used Furman.  At first, I did not have any sonic improvement, though having an UPS is safer for the equipment.

Eventually, I took my volt meter to the unit, and found out that the batteries were worn out.  Replaced the batteries, and got one of the most significant improvements in sound quality.  My wife (perfect pitch, incredible ears, doesn't care about equipment at all so no equipment bias) commented that it was much better after readjusting equipment parameters.

Other than the osiliscope, I don't think you can get a complete picture from any of the other devices above.  Now, I'm going to suggest something I almost never suggest.  I wouldn't bother trying to measure your outlet.  From experience with sensitive scientific equipment, no unregenerated electric source is going to be anywhere close to ideal, so just using a regenerator is kind of a given.

Filtering won't work on its own since there is always line loss, and you are going to always have periods of low voltage.  Having a power company hold at a consistent 60 Hz is also asking too much of distributed electricity.  Some places will be better, some worse, but I can't imagine getting close to ideal anywhere.