Pulse bell peppers and chiles in a food processor to finely chop, then transfer to a 4- to 5-qt. pot. Add 1/2 cup sugar, the salt, and vinegar. Bring uncovered pot to a boil over high heat, then reduce heat to medium and cook, stirring occasionally, until three-quarters of liquid evaporates and mixture is the consistency of loose jam, 15 to 18 minutes.
In a bowl, combine pectin and remaining 2 tbsp. sugar. Stir into pepper mixture and cook, stirring constantly, until remaining liquid is slightly syrupy, 1 to 3 minutes.
MAKE AHEAD: Up to 2 weeks, chilled airtight.