Inner contact: positive + | outer contact: negative -Polarity is fixed.Absolute genius! This adaptor provides you with 9V output from a common USB socket (usually 5V output). Useful for powering all sorts of 9V devices direct from a computer or other USB charging source such as a battery bank. 9V @ 1A rated output when connected to a high power USB outlet. Includes 7 standard DC tips to suit your device.Note:Your USB port must be equipped for high current (2.1A or greater). Some USB ports (particularly those on some computers) are 500mA rated. The device will work perfectly, but will not be able to provide the full 1A current at 9V if connected to a low power USB socket
