I want to start using either an AC or DC adapter to power the radio and I have a question on the milliamp rating. I know that I need 9 volts but what exactly is the milliamp rating for? I have found adapters that are rated for 200, 500, and 600 mA, however this radio calls for 300mA. Will the radio work with slightly lower or higher miliamp rating? and what is the mA rating used for?