Help wanted: USB-C to DisplayPort cable not outputting video on Dell 14 Plus (DB14250)

Hello everyone,

I am trying to connect my external monitor (DisplayPort input) to my new Dell 14 Plus (model DB14250) using a USB-C to DisplayPort cable. The cable supports DisplayPort 1.4 and backward compatibility, and it requires a Thunderbolt 3 or 4 USB-C port.

On my Dell laptop I have the following ports:

• One USB-C port with a lightning/Thunderbolt symbol next to it.

• Another USB-C port with a symbol that looks like a “D” or “P”, and next to it there is also a power/charging symbol.

• HDMI and standard USB-A ports.

My problem:
When I plug the USB-C → DisplayPort cable into the Dell (either USB-C port), the monitor does not receive any video signal. The monitor is set to the correct DisplayPort input.

What confuses me:
The exact same cable works perfectly with my other laptop (a Lenovo Yoga 2-in-1). So the cable and monitor are not the issue.

I am unsure whether:

• I am using the wrong USB-C port on the Dell,

• One of the ports does not actually support DisplayPort Alt Mode,

• There is a driver/firmware setting I am missing, or

• My Dell model requires a different type of cable or adapter.

Could someone please clarify which USB-C port on the Dell 14 Plus (DB14250) supports video output, and whether a simple USB-C to DisplayPort cable should work and the problem might be here? 

Any advice or experience with this model would be greatly appreciated.

Thank you very much!