IF it is your batteries the sulfur smell is from overcharging.
The converter CAN overcharge them if it is not functioning correctly.
AND
Please check your stove knobs to make sure one didn't get bumped open.
What you described happened to me and it ultimately was found out to be propane coming from an open stove knob.
My smell seemed to come from the sink so I thought it was gray tank.
Bottom line propane seeks a lower level. In my case it settled in the sink next to the stove. Didn't set off propane detector because it found the sink first and never went down to the floor.