Heat peanut butter in top of a double boiler or on low heat in a medium saucepan, stirring constantly, until softened; set aside.
Combine sugar, water, and syrup in a small saucepan. Cook over medium heat, stirring constantly, until sugar is dissolved. Cover and cook 2 to 3 minutes to wash crystals from sides of pan. Uncover and cook, without stirring, to 310° (hard-crack stage), about 16 minutes.
Working quickly, pour syrup mixture immediately into peanut butter, stirring constantly, just until blended. Pour into prepared pan. Let cool 1 minute. Score (cut through but not to bottom of pan) into 1" squares. Cool completely.
Cut candy with a sharp knife along scored lines. Dip candy in melted chocolate, allowing excess chocolate to drip back into pan. Cool completely on wax paper; place candy in decorative candy liners, if desired.