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Graphics Options:  Integrated UHD Graphics 610/630
AMD Radeon™ R5 430, 2GB
AMD Radeon™ RX 550, 4GB
NVIDIA GeForce® GT 730, 2GB *Please note that discrete graphics cards are not available on Micro.

Above from the Optiplex 3070 Spec Sheet. 

Hi Team,

Can I add any GDDR5 GRAPHIC CARD TO MY MICRO DELL OPTIPLEX 3070. OR WHICH IS THE BEST GRAPHIC CARD FOR IT? 

Thank you

Hi @ngocngo ,

NONE.  USFF's and micro's have no expansion slots for GPU's.  The only option is the graphics it came with.