Well, it's the 300w version. I was able to figure it out via Reddit, and they suggested a 430w Corsair PSU http://www.newegg.com/Product/Product.aspx?Item=N82E16817139026
This is the post for anyone with the same question as I had. http://www.reddit.com/r/computers/comments/15fza4/need_help_getting_psu_for_inspiron_580/
I have it installed now and it fits without any issue.