I believe that the OP has the answer to the original question. Some conditioners recondition the power. IOW, they take the AC input voltage and current, convert it to DC, then convert it back to AC with a now fixed voltage and frequency that won't change. it also cleaned up the voltage/current. They also may have very large capacitors.
others, take the input voltage/current and filter it to remove noise along with surge suppressors.
for those that think that power conditioners have no value, I say, it depends.
When I hear or read someone who's first words are "I think", I typically walk away. Doesn't really matter what one thinks. facts are what matters. If you take five very good power conditioners and do A/B comparisons versus each other and more importantly against direct wall connections, then listen to the system, you will hear differences.
Keep the power amps directly connected to the wall outlet and the low level equipment, pre-amp, turn table power supply, CD player/transport, music server, etc. plugged into the power conditioner. Then listen. hear any differences?
I have relatively clean power coming from my utility. But, I still heard definite improvements with each power conditioner I demo'd. And I also have and use four (yes four) dedicated lines.
My point is to hear for yourself. Take the equipment home for an in-home demonstration and A/B yourself in your home system. This is true for any piece you want to buy. If a dealer won't let you take a demonstration unit home for an in-home demonstration (after taking your credit card information of course), then something is not right.
Many times the noise floor is lowered by removing grunge on the line. Some remove frequency fluctuations from the utility. This is what turn table speed controllers do. They take the AC wall signal with the 60 or 50 Hz signal, convert it to DC, then convert it back to AC with a solid fixed frequency. You tune your turn table to that frequency and now you have stable speed regardless of what the utility's frequency is doing.
anyway, check for your self. A power conditioner may help.
enjoy