Dell uses proprietary parts (fans, front panel connections to motherboard, 6 pin power connector instead of standard ATX 24 pin, power supplies, etc.). Best option is to reuse the CPU and buy a standard ATX motherboard that will accommodate the i5 10500 (B460 chipset) along with standard ATX case and power supply.  Or sell the 3080 and buy what you really want. You will also need a new copy of Windows as the Dell supplied Windows is only legally licensed for the computer it was delivered with.
Hi, I have an Optiplex 3080 sff cpu i5 10500, i want to replace the case into a tower case, and add 500W power suplly and put GTX 1660 on it, and i want to know with case fit perfectly the motherboard, Waiting for suggestions, thanks,  
dell optiplex 3080 sff motherboard upgrade