Note 9 and dex not consistent

[Android Central Question]

I've managed to get my Note 9 work with an adapter and HDMI cable once or twice. Is there something to do with Developer Options/Debugging that affects this? Or something else? Often when I plug in the adapter and cable, I get 'USB supplying power to attached device' which I can only change to 'midi', 'transfer files' etc - not Dex

 

[Connert]

My first though would be the adapter being used. I have two different adapters and both work perfectly for DeX.