My favorite power supply for Arduino projects that require 5V is an old 5V phone charger connected to the 5V pin. Those chargers are widely available. I buy them from my local thrift store for less than $1.50 USD. Be sure to confirm the 5V output with your DMM before connecting to your project.
Be careful when using the power plug or Vin. Powering through Vin or the power jack means that the Arduino and all peripherals that are on the 5V rail are powered by the onboard 5V regulator. The on board 5V regulator is not heat sinked so will supply limited current before it overheats and shuts down. I would use a buck converter to drop the higher voltage to 5V or an old 5V phone charger and connect that to the 5V on the Arduino, bypassing the, weak, 5V regulator. Then the rated current of the DC DC converter or charger is available on the 5V line.