How to find current drain out of a connected USB device?
You can buy one of these:

Image found here
But bare in mind they are not always accurate (if you buy them from aliexpress like i did, you will end up with a +- 20mA current error.
Another device you can buy (for sure results) is a micro-current measurement device https://www.eevblog.com/projects/ucurrent/

which you can also build by yourself.
And you can also (if you have an accurate Amp-meter) cut your usb Vcc wire and hook the amp-meter in series, you will see how much mAmps it draws.