Your nephew is clueless about electricity but don’t feel bad, most people are.
The disturbances in your 60 cycle sine wave come from outside the home, mostly from industrial loads. We have non-cyclic loads and supplies now that morph the sine wave. A dedicated line will help keep in-house interference off and more importantly, ensure adequate current is delivered to your amp. but will do nothing about the quality of the power.
The Furman you are looking at does nothing to fix the degraded sine wave. Only a regenerator can do that. PS Audio is the rolls Royce there.
I don’t think you have tube gear but most "conditioners" can’t regulate voltage either. a tube amp thrives with the voltage that it was designed to. Once again, a regenerator will allow you to set the voltage. My voltage is 120.0 +/- .1 V.
Now one last thing. Not all amps and components need clean power. It gets rectified eventually for most purposes and some amps and components work fine with dirty power. So results will vary. But tube amps will always work better with regulated voltage.
Jerry