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Adafruit USB A Jack to 5.5/2.1mm jack adapter
This little dongle will let you connect one of our 5V 2Amp or 5V 10Amp adapters to something that expects to connect to USB. The premise is simple - one end has a USB A female jack and the other has a 'standard' 5.5mm OD/2.1mm ID barrel jack with center positive polarity.
It does not have any resistors or other connections inside for the data lines so this won't work for charging an iPhone, iPod or iPad or other device which expects some sort of resistance on the D+ and D- connections. It does, however, work great for Arduinos, BeagleBones, Raspberry Pi's and most other USB-powered gadgets.