That model has a 460W option at purchase, but the only source of PS that will fit internally will be Dell -- anything aftermarket will require an adapter that fits the proprietary plug on the system board and have to reside outside the case, as nothing in the aftermarket is going to fit this case. Whether Dell sells the PS upgrade and whether or not it has the GPU power plug you want  is something you'll have to ask of Dell Spare Parts (1-800-348-6147).
I was gifted a Dell Inspiron 3020 and a Nvidia Geforce GTX 1060. The computer only has a 180 psu and no 6pin cable for a gpu. I'd like to upgrade this. What psu should I get that will fit in the case?
Inspiron 3020, PSU upgrade