Ahhh.... with such a low power draw ..... they make those PSUs custom for their small formfactor PCs. Here's one that won't draw too much. http://www.newegg.com/Product/Product.aspx?Item=N82E16814121397
Good luck my friend, there's almost no PSU upgrades... the most you could get is a 250 watt off ebay. Never purchase those small form factor PCs if you can help it
if you can return the system, I would. There's plenty of mid-tower PCs at the 4-500 price point.