In a saucepan, over medium-high heat, bring the cranberries, 1 cup of water, and 2 tablespoons of the sugar to a simmer. Stir briefly to combine. Cook, stirring occasionally, until the berries begin to burst, about 1 minute. Remove from heat and stir in the jelly; let cool.
Taste and, if desired, stir in additional sugar. Transfer to a serving dish, cover, and refrigerate until chilled, at least 2 hours and up to 5 days. Serve cold.