Does Arduino sell a power cord for their microcontrollers? If they don't, what is the recommended cord for the UNO?
(deleted)
See this link: https://store.arduino.cc/usa/arduino-uno-rev3
I would recommend you power the board from an external power adapter, like those adapters you find on cordless phone changers (not cell phones) etc.
The 2.1 mm mentioned below is the diameter of the inner pin of the power plug. It also states that the center pin should be the positive contact.
Something like this ebay power adapter would work fine. Notice the graphics under the item photo, it shows the center pin is 2.1 mm and the center pin is (+).
Good luck.
Power
The Arduino Uno board can be powered via the USB connection or with an external power supply. The power source is selected automatically. External (non-USB) power can come either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack. Leads from a battery can be inserted in the GND and Vin pin headers of the POWER connector.
The board can operate on an external supply from 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may become unstable. If using more than 12V, the voltage regulator may overheat and damage the board.The recommended range is 7 to 12 volts.