GPU Compatiblity?

[BurningSaturn]

I\'ve been looking to upgrade from a laptop to a gaming laptop, but I have little knowledge on computer hardware. I have my eyes set on a Gateway DX4320-01 but am planning to change the gpu with a Radeon HD 5770, but I was advised that a gpu such as that will need a psu somewhere along 400w.

But another person advised me that my desktop will do fine with 300w.

Do I need to change my psu? And if so which one would you recommend?

Buying a cheap psu isn't a good idea I hear, but what is the least costing but effective for my preferences?

 

[BurningSaturn]

Oops I had made a typo. I had mean upgrading to a gaming desktop.

Which psu ugrade would you recommend? I hear there area lot of cheap shoddy ones... I rather get something worth the money I spend.

 

[BurningSaturn]

My budget can't go over $70 and yes I'm in the US