Rhetoric Camel > 'I don't think it's a small case, I can try to get a picture of the inside of the computer if that helps at all?'

A photo of the case would help determine wether you can fit a standard psu inside or not, but it doesn't really determine wether the motherboard will be compatible with the psu. I think searching around the net for any stories of people upgrading a Dimension 9150's power supply would be helpful if you can't get to a store.