Hi, I'm working on a PCB and my idea is to have 2 different power sources go into the board and it decide which one to use. The PCB is an expansion to another board which has +12v DC on it, both are being connected via a USB cable. I'm going to send the 12v from the one PCB through the USB cable to the other board. This PCB has many uses so current draw will vary based on use. If a person only needs 500ma of power then the 12v from the USB will work. However if they require over an amp of power then they would plug in an external power supply using a barrel jack and at that point the board would use the power from it and not the power coming from the other board. Is this possible? Thanks