Is an older APC backup UPS likely to be the source of blown fuses in new lab equipment?
According to the product specifications, this UPS is not a true sine wave output. It uses a stepped approximation to a sine wave. Here is an oscillogram I captured from a similar UPS:



The screen on the left is the waveform, showing that there may be as few as four rough steps per cycle. The screen on the right is the spectrum plot of that waveform, from roughly 60 to 180 Hz, showing the broad-band noise produced by all those sharp vertical edges.

There is a wide variety of possible waveforms from this type of UPS. I show this one only as a representative example. You will need to capture your own results if you want a definite answer.

The question then becomes, is a waveform like this an actual problem? Some AC-powered equipment will cope with such ugliness easily. Some won't.

However, I wouldn't expect blown fuses to be a symptom of equipment that can't cope with non-sine power. Also, you will only see ugly output like in the oscillogram when you're running on-battery, since this is not an "online" type UPS. When good quality wall power is present, it is passing the wall power through to your lab equipment unchanged.

If you are hearing this UPS click on and off frequently, it means your wall power is not very good, or the UPS's ability to sense good power is degraded.

I would not hold the age of the UPS against it. With the exception of the batteries, which you should change about every 3 years, UPSes tend not to degrade slowly over time. They either work or not. If your lab equipment is staying powered up through a power outage, I would assume the UPS is working just as well as it did from the factory. The only question in my mind is, how well is that?

For comparison, here's what the output of a true-sine UPS I have here looks like:



That output is cleaner than the AC line in from the wall!