OK, so what you are calling an AC/DC adapter is commonly called a "converter" in the RV world. In the world of general electronics it is called a DC power supply, or a battery charger.
Cheap converters, or battery chargers as are often used in the RV world are very low tech. and don't do a particularly good job of charging the battery or providing clean DC power. They often require a battery be connected at their output in order to smooth the voltage. They usually don't have temperature compensation or multi-stage charging as is recommended by the battery manufacturers for faster charging and long life.
More modern, and more expensive converters are true multi-stage chargers and will provide clean DC power even if no battery is present. Some provide temperature compensation and other features as well. The best battery chargers monitor the battery temperature, not the air temperature in the vicinity of the charger. Any good design also has built in protection from overheating. Many have variable speed fans, because even at relatively high efficiency like 95%, they still make a lot of heat when pumping 90A at almost 14V into a battery. They should have access to fresh filtered air, not stuffed in a metal box and left to bake in the sun.
I have had good success with the Iota brand and have used the 75A and 90A versions. They have multistage charging capability either with a built in module, or a cheap external module that you buy and plug in. They provide good clean DC power, even without a battery. They are not temperature compensated, which some will consider a fatal flaw, but if you are using them as a DC power supply then that doesn't matter.
Fortunately most things that are designed to work off of 12V in the automotive world are made to handle a wide range of voltage from about 11V to 14V without difficulty.
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