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You can run any radio up to 14.4 volts safely.
14.2 volts is just fine.
Remember that an automobile's electrical charging system cycles between 13.8 to 14.4 volts. Radios are built around these engineering parameters. Even many base station radios - too.
The 257HP will require about 15 amps though; make sure you use a 20 amp power supply @ 14.2 volts for optimum performance if using it as a base radio . . .
When you look at any "GOOD" Power supply it will have a red slash at the max input voltage well 95% of the time I would be careful if I was you not to toy around with anything over what Robb said.
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