I have high current usage For my circuit as you can see below (link):
I like to power Arduino when it is not connected to PC by USB Connection, So I want to add one external power supply and connect it's GND And 5V to Arduino GND And 5V pins.
So with this new circuit, I have two power supply for Arduino uno as you can see below: :
1-USB Connection to PC
2- Powering the Arduino by External Power Supply and LM7805
So I Asked here about connecting two power supply for Arduino (external power supply and PC USB Connection) and check this circuit Safeness for USB Port of PC or the Arduino.