This one has some sort of RS-232 output, but I
haven't the faintest
what it indicates, other than "your power just failed". I've got the
software for it somewhere, but have never run it.
For older/simpler UPSes, it's quite common for that not to be a real
serial port, but just a collection of status lines (mains failed,
batteries getting low, etc) which can be read over the 'handshake' inputs
of an RS232 port.
And the cable might be strange. It might even have components in it. At
least one manufacturer put optoisolators in the cable (!).
-tony