How to Power Gadgeteer when Usb Client Connected to an not powdered system

how can I power the gadgeteer if I use the Usb Client for keyboard emulator and there can be cases when the system it is connected to will have no power.
as I saw is does not work perfectly when both power and usb cable are connected at the same time.
any solution for this?

I want to have my own power supply but the question if it can work fine having also the power supply connect to the Usb client and also the Usb cable connected to the other computer and runing keyboard emulation on it
I am using this

thanks for the reply
can you please elaborate about what do you mean