No matter which power source you plug in, the Apple Pencil can be charged quickly. If you have an Apple Pencil (Generation 2), attach it to the magnetic connector in the center of the top of the iPad (the side where the volume button is). If you don't see a moment of charging near the top of the screen, make sure Bluetooth is turned on.
If you have Apple Pencil Generation 1
Insert the Apple Pencil into the lightning port on your iPad. You can also charge Apple Pencil via a USB power adapter using the Apple Pencil charging adapter that comes with Apple Pencil.