HP ENVY 17 17-cg0511sa is refusing to connect to Dell PE2723DE monitor over USB - C

[TGBT]

I've just bought a Dell P2723DE Monitor.

When I attempt to connect to this monitor using it's USB -C connection, the display initialises (i.e. starts operating as a display) and then when the USB - C charging starts, it drops the connection. HP System Event Utility is telling me "Recommend using a HP charger"

I've installed all the necessary drivers from Dell and the monitor works fine with my work laptop (which is a Dell) but not with my HP laptop.

My HP laptop 100% does Ethernet, display and charging through the USB - C port, I've done it with this machine before.

[TGBT]

FYI, terminating the HP System Event Utility has meant that it will work with the monitor over USB - C, but is not charging through it, I will keep digging

[TGBT]

After much trial and error (and thinking i had solved it last night) I've found that my laptop will only work with the monitor over USB - C with the HP power supply plugged in. If not, it will kill the connection endlessly, even when the monitor is off and only being used to charge.

My laptop is capable of high power USB - C charging (i've used high power USB-C wall chargers with it before with no issue) so I'm still unsure of why it is causing me so many issues. Attempting "battery resets" by holding the power button when the machine is switched off dont seem to be yielding results either...

[TGBT]

I'm now in a similar position to yesterday. If I have the HP charger plugged in, connect the display USB - C and then unplug the HP charger, after a HP System Event Utility notification for using a HP power adapter. The laptop is accepting power from the monitor (plus working as a monitor and ethernet/usb hubs...)

My laptop was behaving like this yesterday evening, not even ten minutes ago was it doing this behaviour.

Definitely seems like i'm going round in circles. I've set up the drivers correctly so i'm not sure where i'm going wrong. Its also definitely not a case of the laptop not being able to charge off the monitor, it clearly can, its some s/w component that is killing the connection.

EDIT: it was briefly working just on plugging the USB - C in, no HP power supply needed (it did throw the System Event Utility message, but it was charging off the monitor no problem) but now it is back to killing the connection every time when the HP power supply is not plugged in with it