MSI 2060 will fit the case. card dimensions 226 x 128 x 41 mm you have validated that moddiy 24 to 6 pin adapter designed for optiplex 3050/3060 also works for Inspiron 6 pin.  It proves that Dell uses same proprietary white 6 pinout across multiple models from XPS 8940, optiplex 3050/3060/3070/7080, Inspiron 3880/3881 to Vostro 3681 etc.  It is like a Dell DNA.
hello i have a dell inspiron 3881 w the fsp dagger pro sfx 550 watt psu w the moddly adapter and im questioning if i can fit an rtx 2060 ventus from msi 
Graphics card upgrade (dell inspiron 3881)