Upgrading graphics card/power supply

Hi,

I recently bought a Dell XPS 8700 desktop with the specs -

i7-4770 processor, 12GB RAM, 2TB hard drive, Nvidia GeForce GTX 645 1GB graphics card.

I was wondering if this power supply http://www.novatech.co.uk/products/components/powersupplies/nov-psg600.html  would work with my desktop.

Then, I would also like to know if this graphics card http://www.novatech.co.uk/products/components/nvidiageforcegraphicscards/nvidiagtx780series/03g-p4-2784-kr.html would be compatible with the desktop, if I upgrade the power supply to the one mentioned above.

Any advice would be greatly appreciated, thank you.