Cheapish reliable PSU needed for GTS250

[MrBurns]

Hi.

My friend has a dell OptiPlex 755 PC. He has a really crappy ATI Radeon HD 2400 Pro GFx card.
I have given him my old GFX card, an ASUS Dark Knight ENGTS250. He wants to Play Battlefield 3 on Medium settings ideally.

The problem is he has a really crappy dell PSU which I think is only 300w. On the box it says that the ENGTS250 needs a minimum of 450w PSU, with a 12V current rating of 24A.

Are there any PSU's you could recommend for under £50 quid that would power the GTS250?

Also how do I know that any PSU he buys will fit in his case? Are most PSU's a similar size? Im not sure what the dimensions of the crappy dell stock PSU's are.

His pc specs are:

Q6700 Quad core CPU.
4gb of ram

Any advice you guys can give would be greatly appreciated.

Cheers

 

[stulid]

Before you purchase anything,

Check the case will take a ATX sized PSU and its not some custom sized fitment.

Also check the cables dont use proprietary plugs or connectors to the hardware that would only work in a Dell.