How to know if USB-C DP port is working?

That doesn’t work, the device never powers on, it just starts reboot looping. The display power output in theory matches the device specifications. The same thing happens if I try to power from my laptop usb port.

Well, power from laptop usb port is incorrect, the power adapter need at least 15W. When meeting reboot looping problem, I always check to see if the power adapter has enough power.