Question I need help figuring out what to do.

[DELL_Optiplex69]

I have bought a Dell optiplex 390 and a rx 580 and a psu with it but for some reason it wont fit in the case the psu it came with is slim and only has 255 watts which isnt enough to power my rx 580 and everything else in the computer. Also the cables on my psu arent compatible with my motherboard what should I do?

 

[XxDarkMario20xX]

There nothing you can do when things are not compatible with each other only thing is to take them back. Thing about dell computers they have there own desgin off things in there computers. Think only way is to buy new case/motherboard