Electronic – What do I do with the extra “ground chassis” tab on a DC power jack

This might be something similar to the female single channel audio connector where two of the 3 pins will be shorted when unplugged and when its plugged one of those 2 ping will be floating which usually goes to a battery and the remaining 2 pins will be connected to your plug.

This diagram might help you understand better.

Here pin 3 will got to the battery, pin 2 & 1 to the circuit.

When you plug in the socket pin 1 & 2 would provide the power to the circuit and battery will be disconnected.

when unplugged the battery would be connected back to the circuit.

Though there are other configuration also in which it can be used but this is a simple example which might help you understand the way these socket works.

Any long cables with RF clocks/data will radiate noise and when connected to AC ground could also radiate via AC cable from path ground loops.

Smart idea is make generous use of common mode chokes for interface cables and DC outputs to raise impedance of the common mode signals from AC ground.

Beware that Hipot testing of AC/DC PSU may cause failure on secondary port when grounded. This is due to dielectric breakdown of Hipot from primary to secondary. Floating secondary is easier to protect if there is capacitive leakage and tester uses fast rising input. In this case modify Hipot tester to avoid discharge surge that would destruct PSU by using a current limiting series resistor.

Leakage can be minimized with prudent gaps, quality caps, and moisture protection on conductors. (moist dust causes leakage)