Uninterupted power supply question?

So I have ran various uninterupted power supplys in the past with out problem. I always thought that the more stuff you hooked up, the less battery time you would have but assumed that most would run a single computer without problems. I have had ones with auto shutdown before, but I just got two of these

They have a lot more active monitoring, testing etc. built in (basicly simple built in computer control) and it can report several things including load. I was kind of shocked to find that one was running as high as 74% load with just a computer hooked up (and I had some stuff running but the computer was not under full load). So much for adding a pelt to the cpu on that computer with that ups (possible future upgrade)… So I investigate further and found out that it is rated for 330 watts. I was under the impression that this was a decent size ups. I have ran the same computer with monitor on a smaller one that didn’t report load (or anything else) and it never had problems.
So what happens if I go over the rated power (and or over 100% load in its monitoring software)? Do I just get less battery time or do I damage the ups? Is it normal for a 500va 70$ ups to only be rated for 330 watts?

I went looking for info on the old one that was 500va. It aparently was only 300 watts, and it was running this computer, another computer, and a monitor!!! I was running the same two computers that the two belkins are now running and the belkins are reporting 50-60% load for one, and 65-75% load for the other!!! So I ran them both on a little bit smaller one for a couple years or longer and it worked??? If they both ran on a 300 watt model, they should both should be able to run on two 330 watt models even if I add a pelt and it shows power usage above 100%, right? Am I asking for trouble doing that? Anyone know how these things are built and or how they would react to that?