Your video connector is LFH DMS59 [URL] I would recommend ditching that and getting a regular Full height card Optiplex Tower Single slot PCI-E [URL] Or [URL] better is [URL] [URL]    
I need to replace the CG4J5 Graphics card on my Optiplex, which is otherwise working fine. Any ideas much appreciated. Thanks! Here are the specs
Graphics card for Optiplex 780 DT (2010)