RE: 1907FP, Inspiron Desktop 3668, HDMI to DVI PSM issue
Dell never tested the 2016 3668 with this 10 year old monitor so we cannot replicate. Based on your testing, the HDMI out cannot correctly communicate with the old monitor via the HDMI to DVI to activate the correct power save mode. Use a VGA to VGA cable. Or, attach a newer monitor that has an HDMI in port to use with the newer computer.