Took a look at the power supply on NASCARs AMB spot transponder rack which has spots for 20 tonight and is 13.7 volts and was I think around 2.67 amps output. Four wires in cord going to rack but two are negative and two are positive, can see looking at the rack that it is wired this way also, so 12 volts supplied to each transponder..
Thinking should just be able to find a power supply rated around the same, if needed can take a volt meter next just to make sure also.