voltage drop

I have a maxtrac 300, 32 ch, 60 watt vhf low band (42-50mhz). When I connect it to the power supply and tx-rx it seems to work fine. But while in tx the voltage on the power supply drops to 5v from 13.8v. When I connect a 40 watt uhf of the same make, there is no voltage drop. Do I have a bad...