@Dgarretson, OK I get it...if I didn't bridge the boards I could filter 2 batteries or 2 12vdc power supplies. Understanding that the filtering capabilities would be less.
@Celtic66, All batteries will still send some noise down the line, since a chemical reaction is providing the power, to the intended piece of gear. The cap board will help to clean up the noise, hence a better sounding 12vdc piece of gear.
I have a home made cap board between my Optima Yellow Top and the output to the power input for a 47 Labs transport.