rx 580 in Dell Optiplex 990

Absolutely not suitable for an Optiplex with a tiny power supply and limited space. Remember that Optiplex computers are for business use, not gaming. Depending on the version of 990, the psu is as little as 240w  (ultra SFF is 200w) and the requirement for that card is 500w minimum. The biggest 990 tower has 265w psu

Besides checking measurements, check the power requirements/

500W is not good enough.  Power supplies have more than one rail and more than 1 specification of watts.

This is why an EVGA 750B1 works but B2 BQ G2 does not.

Dell has 150W combined power on the 3.3v/5v rails which the video card uses for the 75W from the slot.

Most power supplies BELOW 650W have 100 to 130W max on these rails which is not enough power.

The other issue however is that the Bios in Older Dell models DOES NOT WORK AT ALL with R series cards.

DOS VESA MODE 103 is not available for a card that has UEFI BIOS.

NVIDIA cards do not have this limitation nor do earlier RADEON HD SERIES 2400 3400 4400 6600 7750 8000 series.

Hi @Vilentium ,

Check out this article regarding gaming upgrade on Dell Optiplex 990 MT (notice from the picture and you'll know the writer wrongly title it as DT), installed with a Gigabyte Windforce HD7850 with dimension as 42.5(H)x241(L)x137(W). While your target SAPPHIRE PULSE Radeon™ RX 580 8GD5 dimension as 40(H)x230(L)x125(W), it's smaller in size and should be finely fit into your 990 MT.

And from the picture provided by the writer, the longer Gigabyte GPU may covered the 1st white SATA port on motherboard. But for the 11mm shorter Sapphire RX 580, it should be fine again.

Furthermore, do have Optiplex 990 installed with RX 580 shown in Userbenchmark.

After using GTX 1060 in Optiplex 990 without any issue for 2 years I had to move to RX580.

It works , buuut : 

- very tight fit (I almost abandoned at some point ) very very unlikely would recommend to anyone

- Lots of heat

- I used 720Watt power source with 2x pcie connectors . Videocard is Sapphire RX 580 Nitro + as it draws power from 2 connectors and it will protect the weak PCie power delivery of Optiplex 990

- You MUST install windows in UEFI mode

My honest opinion is that the board is too big and consumes too much power for such a small case. But that's it I did it.

Why I did it:

- I must use a specific monitor (22 inches) and such a small monitor with displayport cannot be found. Since it has HDMI in order to use freesync over HDMI you moust use AMD card . So here it is. 

I’m having trouble getting my sapphire pulse rx 480 9.06 inches in without blocking my sata ports how did you do it. 

I’m having trouble getting my rx 580 in without blocking the sata ports how did you get it in. I have the same sapphire pulse and size as  you. 

I have been trying all night and all through the morning to get my wife's Opti'990 working with an RX570 8GB, while almost everything installs normally and looks great btw...My issue is the HDMI audio device is not detected at all..Yes, power supply is upgraded! And I did check to make sure it was installed in UEFI mode...and it was NOT, would this be my issue?
I have tested everything like a dozen times, the garbage NVIDIA card works fine, however 0 out of two Rx570's had any HDMI audio devices...all work in another PC.
Also, when I tried to manually install the audio drivers the error message said not compatible with my version of windows (even though it is or at least should be)

Also...It is a tight fit but you can trim the fan shroud (least on my 570's I can) and also use "lateral 90 degree Sata cables" <--Google that term and it will pop up...probably newegg or on amazon.