Dell Optiplex 7010 Tower

I have been using this model for simple Photoshop and Illustrator edits and have run into some problems.  Nothing that seems major, but I still feel like it's in my best interest to upgrade my PC's GPU.

What would be the most affordable GPU I can use in the 7010 without having to upgrade the PSU.  I think my PSU is at 180W.  

And if I have to upgrade my PSU, are there any suggestions for someone on a budget?