 Unlike USB, power supplies with a DC barrel jack connector can have different polarities and voltages, making it far too easy to plug the wrong one in and possibly damage your device. To avoid this, let's decipher the printing on a DC adapter. First, there's voltage, 5, 9, or 12 volt are most common, whatever it is, it needs to match your device's required voltage. Then there's the current, which needs to be greater than or equal to what the device asks for, so a bit different than voltage. Lastly, there's the connector's polarity. 99% of devices require a center positive connector, which is usually denoted using this symbol. But watch out for center negative supplies, common in some audio devices. They use a very similar symbol, but you don't want to mix them up.