the possibilities are multiple depending on you have i5 or i7 2nd gen intel cpu. limitations are modern powerful gpu can be bottlenecked by old sandy bridge cpu that is not overclocked (Dell BIOS does not allow user OC). In the past for i7-2600, there was GTX 970 which is still popular, or RX570. for i5-2400, there was GTX 950/960. 1050, 1050 ti, 1060 gpu are also possibilities.  1070/1080 would be too fast for the cpu. e.g., Intel Core i7-2600 (Clock speed at 100%) with NVIDIA GeForce GTX 1050 Ti (Clock speed at 100%) x1 will produce only 3.46% of CPU bottleneck on 1080p resolution. [URL]  
Hi  i have optiplex 790 MT and i installed gt 1030 in it "due to money shortage" a few months ago ..it works fine but i want to know if i can install a modern graphic card later will it work or not ? so what are the possible graphic card upgrades for this system ? and what are the limitations of the upgrade ? " and i know that i should upgrade the psu for that so it's ok " by the way , it's mentioned in the system manual that 790 MT supports full height card Thanks in advance   
all possible GPU upgrades for Optiplex 790 MT