On turning on the Dell USB Type-C display for the first time, the Easy initial setup is displayed. Click Yes, to enable the Always on USB-C charging option.
If you miss enabling the option on Easy Initial setup window, then you can enable the setting using the on-screen display menu available on the display. For more information on enabling the option, see the documentation that is shipped with your display.
NOTE: The "USB-C Always On Charging" firmware option may not be present on all Dell USB Type-C displays. You can enable the USB-C Always On charging feature only after you update the firmware. Download the Dell display firmware, at Dell.com/support.