Computer Power Supply

[PaulM]

I have a table computer powered by DC-DC step-up power supply (12vdc to 19vdc) at the nav station. I wanted to use the computer at the helm, so purchased a 12’ extension cord and threaded it to the pedestal. All works fine at the nav station, but when I plug in the computer to the power supply with the extension it but won’t except the charge. I checked the voltage, polarity, All is good. Any idea why? Are computers particular to the flavor of power to charge?