Question about Dell USB-C to

Using the adapter via Dell XPS 13 (7390). Transmits via DP port but not via HDMI port. HDMI port does not seem to work. All other HDMI adapters and cables transmit without problems. This is definitely not a problem with the notebook. Either compatibility problem (Dell with Dell???) or defective. Has anyone had the same experience? I have now bought the following adapter "Dell USB-C to (HDMI, 15.20cm)" which works without problems.