This USB In-Line Voltage and Current Meter with OLED Display is a lot like the Charger Doctor. Just like the charger doctor, you can use this meter to find out if your voltage is too low or your current draw is too high.
Use the USB In-Line Voltage and Current Meter to measure the working voltage and current output for any USB port and project. . This voltage meter has an OLED display that shows off voltage, watts, amps, and mAH and instantly reads the numbers out for testing devices such as chargers, cables, and cell phones. There's a button on the back that allows you to flip the display 180° for easier reading.
You can use this device from 3.7-13VDC input voltage (although most USB devices tend to hover around 4.75 to 5.25) and up to 3A of current. It's a very handy tool for testing USB devices above 7VDC, checking load levels and debugging battery chargers and boost converters.
Adafruit Product Page: https://www.adafruit.com/products/2690