[This question only applies to using the pin headers, not the EZ connect cable.] In V1E units and later you can plug in all ESCs now because I’ve rewired the board pins to only pull power from ESC Motor-C connection. 

Also, in the older boards you could connect them all together. Since it is in parallel, it doesn’t create 20volts but just 5v with more current capability. Although we often connect batteries in parallel and series, I never see power supplies connected together, It’s just a bad idea. If you have the V1D or earlier, you should connect only one red wire.