Is this the model you have by any chance
https://www.portablefridge.eu/portab...md14f-14l.html
looking at the specifications power rating at 12V is 32watt which is under 3A so you should have no problems running it from your power socket, even looking at the latest model which has a 40L capacity is still only draws 32watt at 12V.
just don't leave it connected to any powered socket while the car is parked up for any length of time with the engine off, it will soon run the battery down.