Dried fruits will usually have more calories and natural sugars per serving because the dehydration process removes so much of the water normally found in the fresh fruit. That missing water is what makes the dried form smaller than the fresh fruit, so there's more pieces of dried fruit in the same serving size. For example, according to the United States Department of Agriculture's National Nutrient Database, one cup of grapes has about 104 calories, and a cup of raisins has over 434 calories. This doesn't happen because the raisin company added sugar, it happens because the raisins take up a lot less space than the fully hydrated fresh grapes. If you look at the calorie content of grapes verses raisins by pieces of fruit, then the database shows ten grapes have 34 calories and ten raisins have 16 calories.
When you look at the nutrient facts label on a package of dried fruit, you'll probably see the amount of sugar that's contained in the fruit. This probably isn't added sugars in the form sucrose (table sugar) or high fructose corn syrup, unless it's specifically listed as an added ingredient. The sugars found in dried fruit are mostly fructose and dextrose, the same sugars that are naturally found in the fresh fruit. However, some dried fruits, like cranberries, are too tart for most people to want to eat them as a snack, so sugar or fruit juices are added to them when they're dried. Make sure to read both the nutrient facts labels and the ingredients list before you buy the dried fruits. The ingredient list on the package will tell you whether the sugar in the dried fruit is added sugar or natural sugar.
Sources:
United States Department of Agriculture - National Nutrient Database for Standard Reference Release 24. "Nutrient data for 09132, Grapes, red or green (European type, such as Thompson seedless), raw." Accessed February 06, 2012. http://ndb.nal.usda.gov/ndb/foods/show/2339.
United States Department of Agriculture - National Nutrient Database for Standard Reference Release 24. "Nutrient data for 09298, Raisins, seedless." Accessed February 06, 2012. http://ndb.nal.usda.gov/ndb/foods/show/2339.


