Just to be safe/sure I would probably go with a 100W rated PSU at the least, such as this one:
http://www.peaktopeakpower.com/catal...ell/s-100.html
Officially the voltage adjust is +/-10%, but my Meanwell 24v PSU goes down to 17.0v with the voltage adjust, and nikhsub1's goes down to around 14v so he says.