My UPS at home just straight up won’t run off of another UPS unless it’s a perfect sinewave. Square wave REALLY makes it mad, and modified sinewave doesn’t work either. No matter what the UPS will refuse that power and only use its batteries.

I can’t find anything on their website about it being sinewave (pure or modified) so I’m going to assume it’s square wave. I’d imagine a high quality PSU found in a server will handle it, but it won’t be happy.