In fact, I ran one when I was overseas and connected a barrier strip with built-in surge protection. The converter in the UPS generated such high spikes, the protection MOVs in the barrier strip tried to clamp them and shorted out. I removed the shorted MOVs and converted the barrier strip into an unprotected unit. The UPS had been damaged but a second one worked fine, so I was able to run equipment with it even when power failed.

The point of all this is that inexpensive UPS units make a signal that is so marginal it actually damages equipment with surge protectors built in. So be careful and check the signal before using it with anything delicate or expensive.