Want to upgrade the graphics card on my my Dell Inspirion 660 computer.

Hello, I currently have a Dell Inspirion 660 computer. I am looking to change the graphics card to something better, so I play more demanding games. I have the minimum requirements for most games, except for my graphics card.
I am currently building a gaming pc (was supposed to get it for christmas) but due to difficulties, I don't think it will be coming for some time. However, I would like to buy the graphics card I was planning on using for that to use on my Inspirion computer. I was planning on using either a MSI Radeon R9 380 4GB or a EVGA GeForce GTX 960. I don't know if they will fit, or my computer will be able to use them, but I would like to know so I can order it. I am also planning on getting a  EVGA 500W 80+ Bronze Certified ATX Power Supply.

If they will not work, can you suggest a different card that will function well? Thanks a lot!