A DIY USB line power meter stick from Electro-Labs:
This is an USB stick which measures the supply voltage of the USB port and current drawn by the device connected to the port over the stick. Then it calculates the power consumption of the device and displays the whole information with the help of the small OLED display on the board. The stick itself is also powered from the USB port.
Project info at Electro-Labs.
Via the contact form.
You can get something almost identical to this for around five bucks pre-built on the Web. They should have added some things to make it different/better like a RTC, Whr/Ahr measurement, and correction for the dongle’s current draw.