I don't think there's a "standard" 12V plug, as for something like that, it really depends on how many amps the circuit you plan on connecting to it will need...
^^^^^^^^^^^ And what exactly do you wish to power? You would be limited to the amount of current load. Maybe some LED inside bed lighting - no problem.If you’re talking a single 12v socket type outlet you will need to determine 12v constant or keyed power.