Let's try this again with all of my incredible wit included...
"The UPS does not have a pure sinewave output."
I let your previous comment (about inductive load kicks making it upstream to and through a wall wart with enough energy to matter) go by because I'm basically a pleasent kind of guy, but c'mon now. ... pure sinewave output. ?!?!?
I double-dog-dare you to justify your implication that an UNPURE (!!!!!) sine wave AC source will have any negative effect on the effectiveness of most Zapper circuits.
(Warning: undeserved poke-in-the-ribs follows)
Unless, or course, it is a problem for SOME manufacturers..........??????????
((Oh, god, now he's done it. Quick, hide the women and children!))