I've been on this forum almost 4 years.  I don't have an exact date, but the 3020 was introduced around 2012, which makes for an old GPU list.  The GPU you tried is meant to fit an MT. As for making GPU work externally - [URL]  [URL]  They also come in different lengths.  
Hi, I own a Dell OptiPlex 3020 and in its owner's manual, there is a list of 4 discrete graphics cards that can be used to upgrade. One of them is an AMD Radeon R7 250 2GB, but unfortunately, it doesn't fit (as shown in the photos). can anyone please explain what went wrong here? The other specification of the card is: SAPPHIRE R7 250 2GB Radeon R7250X AMD Video Card Map 128bit HDMI VGA DVI GDDR5 [IMAGE][IMAGE][IMAGE]  
Dell OptiPlex 3020 discrete graphic cards