Richard Tomkins wrote:
What about using APC systems?

The big APC units (Matrix, PowerArray, etc.) have real power conditioning in them and are pretty decent performers.

The cheap ones are, well--cheap.

Get out your 'scope and look at normal-mode and common-mode noise on the output waveforms (both on an off inverter) and you're in for a surprise. A friend recently started using a Vonage VoIP phone with his cable modem and had to ditch his APC UPS because it was causing all manner of noise when it was NOT on inverter. The small value series inductors used in cheap UPS's and so-called power conditioners from almost ALL vendors use these for RF filtering but the price you pay is increased source impedance of the power line as seen by your power supplies, resulting in an inability to keep spurious artifacts (fed back into the line by switching supplies) from infecting other gear in your system. You need a very low impedance line in order to sink all this hash and 90+% of the stuff people put inline just makes the situation worse.