Never put sugar, as in the powdered or granulated white stuff that comes in a package, into your beer. There is a reason the Bavarians (and eventually the entire Germany) outlawed this practice over 500 years ago - it produces substandard beer.
Water, yeast, malt and hops. Period.
Note that I have added molasses to my stout a few times as a cheap way to increase the ABV. The problem, though, is that it thins the beer out somewhat. Next time, I'll just spend more money and use two cans of extract instead of one.