Testing for Dirty Electrical Power

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.

@bmontani and @jmkrajnik, regarding Power Regeneration, you're referring to a device similar to what PS Audio sells, for example?

I just looked up that piece of equipment.  Yes, that would work.  Probably better if all the extra bells and whistles help.

The one I have is spec'd for 120 V +-5%, which would be 6 volts up or down.  The thing I think that really helps is the 60 Hz is +-1%.  Cycles/second is really critical for timed motorized equipment such as turntables and tape players, though it is best if everything is plugged into the unit.

There is also a real time display for voltage on the unit.  When I went to get the specs. out of the instruction manual, the line showed 120 V.  Usually, that indicator shows between 116 and 119 volts.  Per the specs, voltage regeneration would not occur until you hit 114 V.  That shows that my assumption about Hz is probably correct.

I just browsed the PS Audio manual.  It is rather sophisticated piece of equipment, and it has a virtual oscilloscope built in (a little bit of evidence that my assumption that only an oscilloscope would help with readings.) It has a built in degaussing function, which is helpful.  Though I have a manual unit from The Gryphon.  That cost me under $100, though I did buy it 30 years ago.

The PS Audio unit is a lot more sophisticated that what I have.  There were options to adjust the sine wave, which of course, would affect Hz (hertz is really sinewave/second).  Mine keeps it stable.  That one allows adjustments based on inputs for further optimization.

Since I've never seen (or heard) a PS Audio unit, I don't know if that extra sophistication would help.  Though having the oscilloscope and the degausser built in is nice.  I think it would be better, but how much?  No idea.

I have a P20.  It is an excellent power regenerator.  Very. Very low impedance.  It is like upgrading the power supplies of all of you components.