That is an X2 safety capacitor. Do not substitute anything without this rating. These types of capacitors are designed to be placed directly across the AC utility lines and contain several features to prevent fires and similar hazards. Radio shack probably won't have them, but they're readily available online. The key specs are capacitance (must match exactly), voltage (could be higher than the original rating, but in this application you should try to match it exactly if you can), and finding something that's the same size or close enough to fit. Of course, make sure the replacement also bears the X2 safety rating.