I have an APC ups (a Back-UPS 350 USB, not that it really matters) which I monitor via apcupsd (note that you need a version of apcupsd > 3.10 to make use of a USB cable to your UPS. This doesn't exist in debian woody or unstable; go compile from source)
I have a script here which will output some information from the UPS. The only useful parameters I could get via apcaccess were the Battery Charge, Nominal Battery Voltage, and Time Left, so these are the values that are output from the script. Other UPS's can report on other information such as AC Voltage and Frequency, the former of which might be quite useful.1?
LindsayDruett has just done it on an MGE UPS
The best way around this is to create your own data sources, and enter in the relevent SNMP OIDs.
This was done with a single phase 2 KVA (2000 VA) UPS. (MGE2000 UPS with a 66074 SNMP/Web Management Card)
A rule had to be added into the CDEF functions as the output values were ten times the real values (apart from percentage and seconds).
More SNMP readings can be done, especially on larger installations where three phase and/or external batteries are involved.
Cacti Templates for MGE UPSes can be obtained here
This template will support both Single Phase UPSes and Three Phase UPSes.