Your either blind or making it up. More accurately not seeing the whole picture. If there is a primary to secondary fault, the AC breaker feeding the DC Power Supply in your AC breaker panel is going to operate, or the 8-amp primary fuse inside the DC power supply will operate. It will be a race to see which one operates first. Both your AC Equipment Grounds, and DC Equipment Grounds share the same common ground electrode system. If you followed code and wired up everything correctly the moment the primary shorts out to the secondary, you will have 120 VAC on your coax shield and radio chassis just like you said. However the rest of us should have our coax shields and radio chassis bonded to the Ground Electrode System, and the fault is returned to the utility transformer neutral causing a tremendous amount of current to flow and operate your 20-amp inside your AC breaker panel, or the 8 amp fuse inside your DC Power Supply transformer primary. The race is son to see which over current protection device operates first. Double redundant protection. For some reason you have not seen that yet. Your radio system shares the same common Ground Electrode System connection.