Its a very basic system. Most quality PSUs start at 400-450W, and that is way more than you need currently. Obviously if you are interested in potentially upgrading the graphics card then you may need something larger. Generally speaking though, a quality 550-600W PSU will power any single GPU setup.
A solid entry level PSU like a Corsair CX430 or XFX Core 450 would suffice. Both are 80Plus Bronze rated for efficiency and come with a 3 and 5 year warranty respectively.