In article < XXXX@XXXXX.COM >,
I recently purchased two UPS units, so can give you two points of
reference. FWIW, I don't think either of the units is "noisy", in
the sense that they inject any noise onto the power line, but one
tends to eat X-10 signals (and probably all higher frequency
signals), whereas the other doesn't.
The APC 725 ES did not seem to affect the X-10 signals at all by
itself. In fact, it seems to provide some isolation if an X-10
signal sucker, like my PC, is plugged into it. With just the UPS,
or just an X10 line filter, X10 modules on the same line as the PC
were marginal. With both in line, the X10 modules work reliably.
The Belkin F6C500UNV is quite good at absorbing X-10, so good
in fact that I would not advise using it on circuits with X10
(My old AT&T UPSes from the early 1990's, now on their second set
of batteries but still going strong, are all very X-10 friendly.)
My 2 cents, FWIW.