This USB Power Meter is a versatile little tool that can provide voltage readings down to 0.01V and current to 0.001A, displayed on the built-in color TFT LCD, while your device is connected through it to a power source. You can also measure the capacity and power of battery packs/power banks as well as temperature and cable impedance!
In addition to the main numeric measurement interface, you can also toggle to voltage and current bar graph interfaces (because who doesn't like a good graph?), quick charge identification mode, wire group impedance measurement, and a simple settings screen. And with the recording option, you can easily record your data. Mmmmm data...