Video Card Upgrade

Hi Dell Team! I need your help, I'm the owner of a Dell Optiplex 990 DT (Service Tag:

<ADMIN NOTE: Service tag removed per privacy policy>

) and I need some support, please. I would like to upgrade my video card but I don´t know, it´s very confused to choose one .. I´m worried about de PSU, there´s a confirmation about the performance of the recomended video card on my desktop. I don´t want a desktop in flames, please. 

If you need another information (like photos or something else) about the desktop .. please ask. 

Thanks in advance.