USB outlets are commonly used to charge devices and run small electronics like personal fans.
USB is 5v, unlike the house power system which is 12v. Since the voltage is downconverted for use, USB voltage can remain stable while the van's electrical system voltage fluctuates. The lower voltage means extension cords or long wiring runs may not work well.
Most outlets provide .5A (2.5W), 1A (5W), or 2.1A (10.5W)1).