I notice their different voltages, some are 5v and some are 12v. They are regulated so they could be used for cb or ham radio use, (the 12 volters) it's an easy way to use a mobile radio as a base station. Don't know about a use for the 5 volters. The 12ers they also use them for running tatoo equipment, they can turn the voltage up and down and that turns the speed up and down.
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