Wll the GPU fit in my PC

PS: Sorry for uploading this message two times. I am new here.

That's not the card I would buy imo right now. Its a bit expensive for what it offers. You should be able to find a Radeon HD7850 for about the same. They are also usually smaller.

A good PSU, like the XFX 550W should do.

But i found an old one for 100$ in my land that has 27 months warranty left. The only question that I have is if it will fit in my case. According to the specifications of my case in the website http://www.coolermaster.com/product.php?product_id=2597 it wouldn’t fit because it writes Maximum Compatibility VGA card length: 230mm / 9.05 inch. But according to the manual and the height restriction drawing which are placed on the sites: http://www.coolermaster.com/download.php?action=ViewDow... and http://www.coolermaster.com/download.php?action=ViewDow... the maximum width for VGA Card is 252.15mm and the graphic card should fit (Card Dimension (mm) 245*115*35mm). So what to do in the end?

Is there any difference between cheap and expensive PSU?

There is a huge difference between a cheap and expensive one. Mainly in terms of quality. Most cheap power supplies cannot output the stated power and are definitely not worth getting.

So the XFX 550W should be fine if I buy HD 7850 or the MSI GPU R6870-2PM2D1GD5/OC. But is there a huge difference in terms of performance between this 2 cards, and is it worth to buy the MSI GPU for 100$ from someone who used the GPU which has 27 months warranty?

The XFX is good, and the 7850 is much quicker, but if you are getting the 6870 from a reliable source for $100, then thats a pretty solid deal.