Yes. Something doesn't sound right.
With the information provided I can see the convertor/charger going bad and have a lower dc output which would increase amperage and fry thing on the DC side.
But the Microwave was also fried and it has nothing to do with the Invertor/charger and only the shore power 120 volts.
I say the Surge Guard didn't do its job and allowed high, low or even surging 120 volts into your rig.
I have a Progressive Industries power monitor like this one that I wired into my main cable.