Hi!

Generally[0], UPSes will produce the rated output for 20 minutes,
so if yours worked for an hour, that suggests that your load is
only 333VA.

I suppose that's true of higher end UPS units. However, consumer grade
units run at their full load may only last 3-7 minutes by the
manufacturer's own admission. (I have a feeling that their admission
is also somewhat inflated from the reality.)

That's why I suggest anyone buying an average UPS get one that is
larger than they need. The inverter will also be a lot happier since
it isn't being run so close to its limits.

William