Place 7 clean canning jars (1-cup size), rings, and new lids in a 6- to 8-quart pan. Cover with water and bring to a boil over high heat. Remove from heat; leave in water until ready to use.
Wearing rubber gloves, remove and discard stems and seeds from chilies.
Cut off curved tops and bottoms from bell peppers; discard stems and save pieces. Cut off and discard white membranes; save seeds. Slice straight pepper sides into 1/8- by 2 1/2-inch strips.
In a blender, whirl chilies, bell pepper tops and bottoms, and 1/2 cup vinegar until a smooth purèe.
In an 8- to 10-quart pan over high heat, bring chili purèe, bell pepper seeds and slices, remaining 1 cup vinegar, and sugar to a full, rolling boil, stirring constantly, then boil for exactly 3 minutes.
Add pectin to pan. Stirring constantly over high heat, return to a full, rolling boil, then boil for exactly 1 minute.
Drain jars, rings, and lids. Ladle chili mixture into hot jars to within 1/8 inch of top. (Let any extra marmalade cool, then serve or chill airtight up to 2 weeks.) Wipe jar rims clean. Cover with hot rings and lids.
Protecting hands with pot holders, invert filled jars on a towel for 5 minutes. Turn right side up. Every 5 minutes, turn jars over until marmalade has set and seeds are evenly distributed, 45 to 60 minutes.
Let marmalade cool at least 2 more hours. Serve, or store up to 2 years.
Nutritional analysis per tablespoon.