(Redirected) Alienware X51 R2 graphics card and power brick

Hey everyone i would like to upgrade my graphics card to a 950 witch my dad has had this befor and he had called you guys to know if we can upgrade the card on it and your tech sp said yes we can with a power brick and a limit card is a  NVIDIA GTX 950 and i wish to know were i can get one that has 4gb and were i can get the power brick for it cuz they said we can but as what we found the site only has up to 330 watts not around 400 or more that this card needs to run the sys and card plz help