The question is whether your USB converter gadget can provide enough current to power your Uno.
How much current is your Uno (and whatever else is connected) draw? This can be measured with a DMM.
How much current can your USB converter gadget supply? Do they publish a spec?
If not, do you have the schematic diagram? Does the +5V power simply "pass-thru"?
Is the EasyDriver being powered (5V) from the Uno?