I just got a DisplayPort to HDMI adapter, but it will only work if unplug another monitor. I have an RTX 2060 with 3 DisplayPort outputs and 1 HDMI output. In order to get the DisplayPort to HDMI adapter to give an output, I have to unplug my HDMI monitor, which defeats the purpose. Does anyone know why this is happening?
This is quite common. Two of the outputs are ganged - they are not distinct outputs, but shared. If you're not trying to use all four ports, you should be able to use one of the other DP ports simultaneously with the HDMI.
You'd need to check the manufacturer's site for further information [this is often quite well buried].
Note NVidia is not the manufacturer, they only make the graphics chipsets.