Power conditioner or not?

How do power conditioners work? 

I assume they try to filter out variations of voltage but it's AC in and AC out.

They also must have a circuit breaker to try to block spikes in voltage caused by lightning or other big shocks. 

I am confident that most quality equipment designs in beefy transformers,  rectifiers and filter capacitors that handle most anything they are likely to encounter.  

My experience, with the PS20 and 15 is pretty good, my soundstage and clarity improved, as it did and measured distortion. 

My high power hungry Class A amp opened up and became a lot more dynamic.

In the USA I would grade the results about 7-8 out of 10, in Spain 6-7  out of 10. Maybe the difference is between 110 and 220?

I recently had a highly reviewed power conditioner in my system. I heard a constant boinging (odd word I know - but descriptive) sound constantly and quite audible hum all the time. Decided to make my own power distribution unit with high quality receptacles, cast aluminum boxes, and star wiring. I do have a Deep Core 1800 in front of the distribution unit. Deep Core eliminates DC induced by motor loads and only minimal EFI/RFI filtration. I could not believe how much quieter and better my system sounded. Hum and other spurious noises disappeared completely. Count me as one who does not support full blown power conditioners. Is this simply another way to keep audiophiles spending money for something they do not really need and often make a system sound worse.?