Regardless of the electronic device, it is important to check the cables to see the quality of the electricity: stability, voltage, amperage: Tip: How to measure the intensity of the charge current or How to check the quality of a USB cable
However, for large cables, it is relatively easy with a classic voltmeter to check the voltage and voltage.
For a USB cable, it is slightly more difficult, these are small cables and plug / USB tip is not designed to insert something other than its USB compatible partner.
The concerns of these, is that they are limited to maximum 10V. USB in General, it is the 5V, so voltmeters have a good margin.
On the other hand, lately, there is the USB type C, but this one can go up to 20 V!
So it took a new dedicated voltmeter to support the 20V, and I found one: the Satechi ST-TMPC Power Meter
This little gadget can indicate 4 data: voltage, amperage, mAh and the direction of electricity!
It's easy to use: you plug the cable on one side, and on the other, you plug into the device.
In short, it's really not rocket science!
This allows you to check the quality of your cables, your device or even your source! Enough to detect your energy problems or energy transport!
How to use it: https://www.dropbox.com/s/9jzfetno06nm4jn/Power%20Meter%20.pdf?dl=0%20%3Cbr%3E%20