How to know USB Current and Voltage

You can get the answer for your question about USB Voltage and current with this small tool, for example why charging process in the USB devices, smartphone, power bank, etc, will take a long time or short time, You can know voltage of the USB port of your computer/laptop, USB charger and know the current flow from USB port to USB devices.

The name of tool is USB tester, it can measure Voltage and Current of USB port,

To use this tool is very easy, 
Plug the input port of this tool to the USB port of the computer/laptop or USB charger.
The output of this tool to be connected to the USB peripheral, Handphone, smarthone, flash drive, external hard drive, etc.

For easy to understand you can see the figures below:

In this example I put the USB tester between USB charger and my smartphone.
Voltage of this charger is read  5.03 V (with load ).

USB tester displaying the Voltage of USB charger

For the model of this USB tester, wait for several second, to toggle/change display from Volt (voltage) to Ampere (current), and from Ampere to Volt.
The electric current flow from charger to my smartphone, the value is 1.05 A

USB tester displaying the Current in Ampere of USB charger

I try to move and plug the USB tester to my Laptop.
The value is 4.86 V (with load/smartphone)
USB tester displaying Voltage of  Laptop USB port
The current flow from my laptop USB to the smartphone is 0.46 A

USB tester displaying the Current in Ampere of  laptop USB port to the smartphone
I try to connect to my Flash drive, the current is 0.04A

You can try to your USB devices, The price of this small USB tester is very cheap, you can buy from online store or at your local computer accessories store.