The USB Power Current/Voltage Tester from Brando lets you easily measure USB power and device operating current/voltage. Just plug the small USB adapter between the device and your computer or AC outlet and the built-in display shows current and voltage. It will work with smartphones, tablets or any devices with a USB charging port. It is able to read voltages from 3.5 to 7V and current from 0 to 3A. The USB Power Current/Voltage Tester is priced at $10 and is available from Brando.