The Ultimate Guide to Powering Your Arduino Uno Board - Tech Explorations
Fleeting- External reference: https://techexplorations.com/blog/arduino/guide-to-arduino-uno-r3-power/
can accept an input voltage range of 6 to 20 volts. Internally, the board regulates this voltage to meet the proper functional levels of 5 and 3.3 volts for its components and connected peripherals.
— https://techexplorations.com/blog/arduino/guide-to-arduino-uno-r3-power/
A 12V AC-DC adapter with a 2.1mm centre-positive plug is sufficient when you’re near a wall socket, while a 9V battery can be used for portability when working in remote locations
— https://techexplorations.com/blog/arduino/guide-to-arduino-uno-r3-power/