dell P2715Q, MacBook 2016, flickers/blacks out

When I try to connect my new MacBook 12" 2016 with a Dell P2715Q through the hdmi cable and the Apple HDMI/USB-C adapter it flickers or blacks out.

I tried different hdmi cables (that works), two HDMI/USB-C adapters, cleaning up the PRAM from the mac and resetting to factory settings on the monitor, but no improvement.

According to Dell Support, the adapter is limiting to =

1920x1200 60Hz
3840x2160 30Hz

So how can I verify that the Hz setting for the resolution is correct in the Apple OS?

As a workaround, should I go for a Display Port connection to the monitor:

USB-C/3.1 to Display Port adapter (CableMatters)

3840x2160 60Hz, MST
Apple USB-C/3.1 --> USB-C to Display Port adapter --> DP to DP cable --> Monitor DP in

Thank you!