The voltage drop on the circuit feeding the fridge is a likely culprit to many poor amazon reviews. To be 'portable' and convenient( marketable), they have to include a Ciggy plug, but the ciggy plug itself is an insult to DC electricity as it has so much resistance on a circuit with only 12.x volts pressure to begin with.
Basically the higher the voltage which reaches compressor controller, the better the fridge will work. Equate it with driving on tires with just 22 PSI versus ones with 50PSI. Sure the tires still roll at 22 PSI but it requires more power to move them, and the tires will heat up, wear out that much faster when under inflated, while wasting fuel in the process.
So go pump up your tires.
Cut off the ciggy plug and wire it directly over the shortest possible wire run to fuse block over 10 or 12 AWG wire.
If one insists on the Ciggy plug/ receptacle, at least get a quality one like the Blueseas, and wire the receptacle with the shortest possible wire run to fuse block with 10AWG.
https://www.amazon.com/Blue-Sea-Systems-Volt-Socket/dp/B004XIWF12
The quality of the ciggy plugs provided with so many 12v items is criminal, and does not take into account the 12v receptacles are usually very underwired to begin with. Combine these factors and Dismal is the resulting performance, if the fridge even switches on in the first place.
If the fridge does not turn on when plugged into a 12v receptacle, try starting the engine. If the fridge does then turn on Voltage drop is most definitely the cause of in operation. The fix is fatter shorter cable to fridge, and a ciggy plug cut off, smashed into a thousand pieces with the biggest hammer one could find and vent all their frustrations upon.