You can power the Arduino Uno/Nano using the following:
Barrel Jack (for UNO only), it is connected to the input to voltage regulator.
VIN pin, it is also connected to input of voltage regulator.
5V pin, it is connected to the output of the voltage regulator and directly of 5V of Atmega MCU.
Finally, the USB.
Is the positive supply of the USB port of an Arduino is connected to the 5V directly? I tried to use a connectivity test using multimeter but it is not connected.
Moreover, it is mentioned in the Arduino documentation around the internet that if you powered the Arduino via USB connection, the 5V pin will be limited to 500 mA only. What if I use an AC to DC adapter (2A output current) that is connected to the USB port of the Arduino, will I will still get only a max of 500 mA? Or if I use USB 3.0 that can supply 900 mA, will I still get 500 mA max for the 5V pin? I read that the polyfuse is the one that is limiting that current.
I have used Arduino Uno and Nano for a long time but I just became aware of this basic concepts when I made a project that should compute the overall power consumption of the device.