Firstly a warning. We are dealing with mains power here, do not get involved unless you know what you are doing.
The only truly effective way I know is to view the waveform on a scope, you will be able to see the shape of the waveform and, if calibrated, check the actual voltage though this is easy to do with a meter.
My interest in the regenerator is to cure a sagging voltage problem in a foreign country, not really about interference so I guess this is different. If your mains is poor, read up on product from IsoTech and Isol-8.
Very much on topic though is that, I have an apartment in a small gated complex, lost all power when the lights in the grounds were switched on at dusk, the automatic switch on tripped the power.
The power supply for the grounds had to be shifted to another supply to cure the problem. The moral being that it is usually best to tackle interference at source, the isolating transformer suggested above being a good place to start.