Good information. This unit appears to be very similar to Lloyd's Quad.
As a suggestion, could you not have a 4 pole - 4 position switch to switch the outputs rather than having to unplug and plug wires every time? Just a suggestion.
10 volts is easy to get from a 9 volt battery using boost regulator. Our ParaZapper UZI delivers a constant 10.5 volts with plenty of current from a 8.4 volt rechargeable, even when it goes below 6 volts.
While electric shavers use a wall wart, they do not apply electricity directly to the body. Always use an IEC 60601 rated supply for direct connection to the human body. There is a reason that this standard exists.