dell vostro 3888

I have a Dell Vostro 3888 I have Been Wanting To Upgrade It But The PSU Inside It Is pretty Small It Isn't a Cube Like The PSU I am Buying It Is A cuboid But a Small One I searched All over For its Name But I Couldn't Find It All I know Is The Psu Was made By Dell I Have a Pic For Reference Btw...