This is a small UPS probably built to a competitive price so don't expect too much. Most UPS units are used to Power a load that consists of IT equipment.
Typically, with modern IT equipment, you find it imposes a leading power factor (capacitive) load on the UPS, 0.9 leading is typical.
There are many technical reasons for this, you can find out why if you want to! But I only suggest you do this if you like really boring technical stuff.
So your UPS must handle the load power factor, you may have bought one that is designed for a lagging power factor, and if you have, it might get a bit warm with a leading power factor.
What you need to know is whether your load is within the "capability" of the UPS, the following link gives a good explanation.