Dell Optiplex 9020M (regulatory model: d09u) - Power but no video.

Try clear CMOs setting via motherboard CLR cmos jumper

Remove power from system.  Look for a blue jumper and use it to clear CMOS.

@Chino de Oro​ Already tried that 

@redxps630​ I did try that - no change.

Did you upgrade memory when you said installed 16 GB ram?

If memory was changed, remove new ram and put old one back to test.

Re: the power light is on *amber) and not blinking

Steady amber = “PSU is working but failed to fetch code”

It may be a bad motherboard if clear cmos: no change

Try a different 19.5V Dell AC adapter if you have one that is 4.5 * 3.0 mm tip

I've tried 2 different adapters (one brand new) and I've tried with the original single 4 GB dim - same results. 

 

looks like the motherboard is bad.