Does a USB port provide enough power for my LED project?
The current draw of one WS1812B is approximately 50 mA each (source). Twelve of them will draw as much as 50 mA * 12 = 600 mA in the worst case, which exceeds the limit (500 mA) that can be drawn from a normal USB port.
It may be possible to use a USB power supply, but you will need to communicate with it to request a higher current limit, which leads to extra complexity.