Currently having the same problem when i plug in my gpu Do you have any clue about the reason or the fix?

Hello @the baz I've been having this same issue with a different behavior on my Optiplex 9010. 1. I would press power button but would not POST, amber light would start blinking pattern 2-1 (bad mb). 2. I have a workaround to power on as normal. I basically hold the PSU test button and sometimes fans go crazy and I have to disconnect power cable and try again. Sometimes I press power button and turns right on. 3. When powered on. And I turn off the computer. It would normally turn on if the power button is pressed before a certain time (say 30min-1hour after shutoff). This would happen even if left on sleep mode. But after this certain time, it would show the same amber light and no POST again. AND REPEAT... I must add that I have changed the CMOS battery and ran hard reset (draining power and do CMOS reset) about 5-7 months ago and my computer worked flawlessly until recently this past month it has had the same behavior. (Last amber code was different as well, 2-3 if I can recall? But no certain) I came to the thread because it seems we aren't the only ones experiencing this type of issue. I will try CMOS replace and hard reset today. Could you please keep me (us) updated on the new PSU replacement? I am suspecting that this may be a factor of failure in my PC due to all the electronics plugged in on same outlet. I will do some testing also, will keep an update on this post. Thank you!

Your 290W PSU is just fine for your GPU.  Even if you went thru the trouble of upgrading PSU's and wanted to use a higher watt GPU, you'd still have to use low profile single slot cards with their own power cable.  I think your setup is just fine as long as your happy with your GPU. If your still curious about optional PSU's, '9020 MT PSU' can be used for a search term in Dell Community and you could Google it as well.  Chances are optional PSU's for the 9020 was already answered.  @speedstep is an expert at it.

'White Light Power and Storage Blinking'  Not sure what you mean by 'storage.' Is the white light blinking a pattern, or just blinking?  Is it blinking orange at all? I take it your PC is not booting to OS.  Do you even get the Dell logo?  It is smart to test with the PSU test button with PC off.  But green light and spinning fans doesn't necessarily mean PSU is good.  It does mean, however, that your internal peripherals are good. First try:  How to Perform a BIOS or CMOS Reset and Clear the NVRAM on Dell Computers  When you do this, replace the size 2032 CMOS battery with a new one.  Bad batteries can cause boot problems.

https://youtu.be/a2sm1SsvQNU

Typically is a mobo failure even if the diags say cpu. If in warranty then contact dell.