electronic timers and modified square wave inverters

I'd be interested to hear from someone who is successfully running an
electronic timer from a modified square wave inverter. Ive got 2
jaycar inverters (200w and 300w model) and the electronic timers
almost cook themselves within about 2-3 minutes of operation
off the inverter (one particular kambrook timer gave off a burniung
smell within about 10 sec of plugging it in). Im assuming it must be
related to the timers power supply not being able to handle the
modified square wave output. Ive tried that same thing with an old
mechanical timer and it doesnt seem to have the same problem
(ovbiously the mains directly drives a mechanical clock with thsee
timers).