AC adapters convert alternating current from a wall outlet into direct current. Modern mechanics use these adapters to run OBD2 scanners, battery chargers, and workshop laptops. Without them, sensitive shop tools would fry from high-voltage wall power.
Using the wrong adapter can ruin electronic gear. The adapter must match the tool's required voltage, current, and plug polarity. Using a 12V adapter on a 5V tool will blow its internal fuses or melt circuit boards.
In electric vehicles, the onboard charger acts as a large AC-to-DC converter. It takes AC power from home or public chargers and converts it to DC voltage to recharge the car's traction battery pack.