I cause my own problems most times. but I don't think it's this time.
I took an old APC 550VA UPS that had a dead battery and wired the battery leads to a cigarette lighter plug. I wanted to make it into an inverter to get 120V in the car. I have a couple inexpensive inverters but wanted to try this with an old UPS. I had opened up the UPS and broke the buzzer so it's not beeping when running on the car battery.
Checking the voltage coming out of the UPS when running on the (car) battery via the cig. lighter jack, it said 90V. (with both an old sears craftsman digital VOM and a new Harbor freight digital VOM).
I took an unmodified similar but newer APC UPS and measured that with AC power (120v) and when it was on the internal battery (around 90v like on the UPS I modified).
I plugged in some transformer bricks and USB power adapters and they put out their rated voltage (12v and 5v).
I don't have an olliliscope... is the 90v because the UPS makes a different wave rather than the sine wave from power outlets and that looks to cheap VOMs to be less than 120V?!