[Quick question] - Power supply to match case

Hey there.

I'm having trouble finding a power supply that matches the physical dimensions of this case. I've tried multiple ATX power supplies but they all seem to be JUST a tad to big to fit safely in the unit...

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

This is my case, I have never come across anything like this before so I'm not sure if I'm just overlooking something small. ANy recommendations would be appreciated.

* Also, it's a midrange gaming system so 500w+

Thanks in advanved!