This little gadget — about the same size as a largeish bar of soap — feeds 4A to your laptop at 15, 16, 18, 19, 20, 22 or 24 volts from a car cigarette lighter. 6A for 20V or less.
Better yet, it runs cool. Not bad for a bump-it-up switched-mode power supply.
I got mine from Altronics, who do mains versions as well.
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