I'm looking for a decent fridge with a 12V-outlet to use in the car for car camping. When I say fridge, I mean something that can keep products cool at 4°C/39°F, regardless of outside temperatures, so that it can be used to transport, for instance, meat.
What you want is a so-called 3-way fridge, generally called that in North America at least, because they can generally be powered by 12V, 110V or propane gas. Presumably similar items exist in areas with 220V or other electricity standards, and perhaps other burnable gases like butane...
They cool very well, and have a thermostat and will keep things quite cool and fresh. Do put it in the shade if it is hot/sunny, however.
Camper Trailer Tech Tips provides a very detailed overview of how they actually work, in all cases however, the electricity or gas is used to heat up one end of a sealed ammonia absorption cycle cooling system. Note: they do need to be kept basically level during operation.
A local RV depot is likely your best bet for purchasing something like this, although google hits in Canada include Home Hardware (a smaller retail DIY chain) and some other stores catering to off-grid and remote living. The model listed at Home Hardware is from Unique appliances, who seem to have a few models to choose from.