external power source

Hi, this is a simple one, and I can imagine you answered it in a million forms but before I do anything irreversible I thought I'll ask.

Is it possible to use an usb mobile phone charger to be used as an extra power supply for the mux board? 
The case is the following:
- JP7 and JP6 is wire 1:1 meaning all the subchannels are going to be powered using the computer side pins as source
- the J1 grove connector is used to hook the mux board to the base i2c bus
- the end of the usb cable is cut off and the VCC, GND wires connected to JP1 3,4 respectively - computer side pins

The real question is: Can I just simply connect that external power source as I described to the JP1 pins and that's it?  I don't want to fry the board considering the mux board is already getting power through the grove connector. 
On the other hand the setup "feels" comfortable and purposeful.

I was waiting for nearly two months for the board to arrive, my favorite and central component, and I'm more like a software guy.
Gimme a go!