The USB-CEC adapter and Intel NUC CEC adapter can automatically power on an HDMI-CEC compatible screen when the PC powers on.
This only works if USB is powered down. You may have to disable USB charging in your PC's BIOS settings.
This feature requires a recent (v9 or newer) firmware. The firmware can be upgraded, if required, by following these instructions: Upgrading the firmware of the CEC adapter
To configure the power on feature, first install libCEC 6.0.0 if not installed already: libcec-6.0.0.exe
Then click on the Windows icon, type "cec-tray" and start it.
Click on the Power Control tab and enable the setting Power on the TV when the PC starts:
Then click on the button Save configuration.
The adapter will now send a power on command to the TV whenever the PC powers on.