Smaller plug-in AC Purifiers -- Shunyata, iFi, Puron...something else? What do you like?

my system was plenty noisy. i tried the ifi AC purifier. tried it every way they suggested. it did absolutely nothing.
isotech isobar and the 4-outlet richard grey help. 

Just curious: using a Monster Power HTUPS 2700 Home Theater Surge Protection and UPS. 

Does it do anything to reduce noice, improve sound, or just a glorified UPS and surge protector?

Furman P-1800 PF R

another vote for Furman, you want the PF R version, has 45A reserve for instant peaks of program material

Usually on sale somewhere, now B&H

I do like the big units due to volt reg max min and surge protection it has save big bucks on shutdown during stoms.they live to sing another day.

Put a Furman Elite 15i on my system.  Helped the sound.  Then I went on a mission around the house and plugged the chargers and lamps, etc into Furman PST8.  Electrical noise goes either direction in the wiring but still the idea of blocking it with a filter makes sense vs plugging a passive device into a common outlet.  I currently have 3 of these PST8 AND the 15i.  A very nice improvent for not much money.