Hi!
We have some critical lab equipment, which we want to power through a UPS in case of mains power interruption. Our UPS is an Eaton 9PX series with 1.5kW max. but typically much less of protected load (100-200W). Everything works fine except for one device, which really doesn't like the AC power provided by the UPS but works fine directly on mains power. This device is basically a high-voltage supply (<10kV), which takes only 70W of mains power during normal operation. When it's powered by the UPS, the high-voltage supply still works but it can't stabilize the HV output, i.e. it fluctuates heavily. When switched back directly to mains (e.g. UPS set to bypass mode), it stabilizes immediately (behavior is the same with or without power cycling).
I assume the HV is directly derived from the AC mains input without an intermediate DC conversion step and is thus very sensitive to the mains waveform. Before getting the company involved and losing sanity to tech support, I want to try to find a simple solution first. The UPS is more or less decent and is supposed to output a clean AC sine waveform, so I measured it with a scope (under light load, i.e. with the HV device connected) and compared it to the mains from the wall (we have 230V/60Hz here):
Red: mains AC from the wallBlue: AC output from the UPS

The sine output from the UPS is actually cleaner with less harmonic distortions than the mains from the wall, but it clearly has some small but significant switching ripple at 19.2kHz, see the zoomed bottom image, with an amplitude of a few volts (roughly 1-2% or so). I don't have much experience with UPS but I suppose it's nothing out of the ordinary, as UPS are primarily meant for IT stuff with their switching power supplies, which don't care much about the input waveform anyway. I can only assume that the small high-frequency ripple is the reason why our high-voltage supply has problems with it.
My question is: can this 19.2kHz ripple be sufficiently filtered out in a simple way? I guess a low-pass filter with a high enough power rating should do but I really wouldn't want to cobble together some custom solution because I have very little experience in playing around with mains power. Maybe that's a common industry problem that has been solved many times already but I don't know where to start looking. Could it even be as simple as putting some ferrites around the cable and what specs would I need?
Thanks for the help!