The USB charger doctor in-line volatage and current meter is a simple and effective way of checking the voltage and current output from a USB port to another device.
Use the USB charger doctor to measure the working voltage and current output for any USB port and project. This blue plastic dongle plugs between a USB device, and passes the data lines through. There's a 0.05 ohm resistor in line with the power pin that is used to measure current draw. The Doctor's digital display instantly reads the numbers out for testing devices such as chargers, cables, and cell phones.
You can use this device from 3.5-7VDC input voltage (although most USB devices tend to hover around 4.75 to 5.25) and up to 3A of current. It flips between voltage and current readouts every 3 seconds or so. It's a very handy tool for testing USB devices, checking load levels and debugging battery chargers and boost converters. It's a little chunkier, but more numerical than our USB Power Gauge Mini-Kit. It's also not open source so check out the USB Power Gauge mini kit if you want to hack together your own power gauge indicator.