As far as I know, cigarette lighter connections in cars are quite "low-level"; i.e. they're not a source of clean, well-behaved 12 volt DC that you can treat li

As far as I know, cigarette lighter connections in cars are quite "low-level"; i.e. they're not a source of clean, well-behaved 12 volt DC that you can treat like e.g. the 12 V rail of a computer's PSU. Instead, the voltage can vary depending on the state of the car's engine, the car's battery, whether or not you're currently hooking up a second battery in order to jump-start your car, and so on. It's not very sophisticated when considered as a source of 12 V DC, since it has these other parameters that are not something you'd generally expect a clean and simple power source to have.