USB Charger Doctor - In-line Voltage and Current Meter It can measure the USB-powered devices empty and easy to use and practical. Compact and easy to carry, no additional power supply, plug and play. Can measure usb interface, cell phone charger, u disk and other products or power supply situation. Detect any USB charger such as PC USB, home charger, car charger. Wide range of applications, any phone, any electronic product, Easy to use.