If your converter/fuse panel is like mine there's fuses and circuit breakers. In mine the far left breaker is one for the converter (power supply/charger). I turned mine off about 3 years ago. When the trailer is in it's nest I use a battery
maintainer to keep the battery
up. The charging circuit in the American converter is not very good, but the battery maintain does the job, plus when I'm traveling the tow's charge line keeps the battery charged. When the trailer is sitting for more than 4 or 5 days my small solar panel
recharges the battery.
Short answer you can unplug it or just flip the circuit breaker.