Is possible to power from an external source (via the plug) the ChipKit PI connected to a Raspberry PI with 12Vcc ? Reading the board datasheet it seems possible as the 5V power supply (the first stage regulator from the external power source is NCP1117ST50T3G, whose data sheet tells it can support up to 20V of external power but I like to be sure to avoid to fire the ChipKit PI.
The following image shows the power supply session of the datasheet.
Thanks in advance. Enrico
You are right! You the 1117 regulators can handle inputs of upto 20Volts and in this case you just have to change the jumper config to use the external 12V jack. There is also a diode for reverse polarity protection which will be useful if you accidentally have a DC jack input in reverse polarity 
As long as you are not drawing a lot of current from the Chipkit Pi, the regulator should stay cool and produce the required 5V. You can even power the RPI from it BUT if the RPi takes say 400mA and your ChipKit Pi takes say 100mA, then half an Amp times 12-5=7 volts drop across the regulator means 7V x .5Amps = 3.5 watts dissipated as heat!
Experiment and see how it works 
