I have a Belkin 350VA UPS with a quasi square wave output. Its output works ok for my computer, but it doesn't work well all with non switching power supply load. An incandescent lamp flickers badly. A fluorescent lighting with inductive input(magnetic ballast or commercial grade electronic) causes the ballast and UPS to make a noise that sounds like resonating and flickers very badly. The output waveform is very elastic and it jumps around on the scope screen.
The output waveform on my 300W quasi squarewave inverter is much rigid and it has no problem running non-switching power supply loads.
Is there a quasi-square wave UPS that can at least stably power anything my power inverter can?
By the way, there is a dead obvious difference in the inverter circuit between the two. The power inverter uses a few ferrite core high frequency transformers. The Belkin UPS have a low frequency steel core transformer that is used for both charging and inverter transformer.