9020 uses proprietary 290W power supply. [URL]   GeForce GT 1030 2gb  Dell 8CCF1 would work. More than that requires the OPTIONAL 365W power supply. 7VK45 365w, HuntkeyT1M43 365w, Delta 365w PSU =Huntkey  CN-07VK45       HU365EM-00Delta      CN-T1M43         DPS 365CB DVP9W Nvidia GeForce GTX 1050 Ti,  4GB, 75w36V90 Nvidia GeForce GTX 1060, 3GB, 120w24K8H Nvidia GeForce GTX 1050,  2GB 75w8CCF1 Nvidia GeForce GT 1030, 30w1MPR3 AMD R9-360 2GB, 75w24K8H Nvidia GTX 1050 2GB, 75w Any non dell cards will require secure boot OFF in bios. disabling “Secure Boot” is enforced policy when installing 3rd party (NON DELL NON WHQL) hardware or drivers MSI GT 1030 for example [URL]      
I have a Dell Optiplex 9020 Mini Tower Desktop with Intel i7-4770 CPU [NAME].40GHz (up to 3.90GHz according to Amazon where I bought it from) and 32GB RAM Speed. I want to buy a graphics card for it but not 100% sure what kind, my last desktop was an Alienware gaming pc so I didn't need to buy one. I used CPU-Z to run the specs and this is all it has built in. Https://valid.x86.fr/f6e9at  Thanks ahead of time. 
Dell Motherboard 06X1TJ different Graphics card support