Vostro 270 Mini Desktop , Power Supply

Hi so can someone pls tell me which PSU is compatible with My Vostro 270 PC? bc i wanna install a GTX 650ti Gpu on vostro 270 but i'm not sure if i purchase an 500watt psu and then it ended up not fitting in my pc , so please comment if u know know something..  i posted pictures of my pc case and powersupply so pls tell if any psu i can use..