Even the makers of Xtend do recommend other sources of energy. Here is an excerpt from http://www.bodybuilding.com/store/sv/xtend.html
Q: Are there any other products that will help improve the results I achieve when using Xtend?
A: Xtend was formulated, and then recently reformulated to remove the need for additional ingredients while you train or compete. However, Xtend was explicitly formulated to contain no carbohydrates or sugar so that you could dictate how you may want to manipulate your carbohydrate needs based upon your training cycle or duration. Therefore, when carbohydrates are desired, combine Xtend with up to 0.45 g of carbohydrate per pound of bodyweight, per hour of exercise. When carbohydrates are added, increase the amount of water used per serving so that the finished formula concentration is easily digestible during exercise.
For myself, who needs to stay away from sugar for health reasons, I keep my simple carbs down, and it works fine. If you want to add simple carbs, and you're not concerned about the effects of too much sugar, go for it. Just don't let our First Lady take it away from you, LOL. Personally, I haven't found the type of energy that comes from sugar to be that beneficial. I like the sustained type better.