PSU

[Casterina]

My budget for a quality PSU is £50-60, I'm looking for one that is 550W with a fan at the back not on the top

 

[Casterina]

This is the case that I have,

http://i3.lulzimg.com/86fcb16464.jpg

If I use a normal PSU that has a fan on the top of the PSU, will the ventilation still be good?