External monitor not detected with USB-C adapter

Just for the record, the adapter started working again without any software manipulation. I've been playing a bit with the cable, at the junction between the small cable and the adapter. So the problem may have been due to a bad contact in the adapter.

There is now an additional line in lsusb:

Bus 003 Device 003: ID 0835:2a01 Action Star Enterprise Co., Ltd

Hope this can help someone else

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Additional note: 6 month later, while manipulating the cable once more to solve the same problem, I just broke it completely. So be careful and consider returning the adapter to Dell before breaking it, if it is still under warranty.