Combine vegetable stock, ancho chiles, plum tomatoes, onion, red chile, garlic, brown sugar, vegetable oil, cumin, kosher salt, and black pepper in a saucepan; bring to a boil. Boil mixture for 2 minutes.
Cover saucepan and remove from heat; let stand for 10 minutes.
Pour mixture into a blender no more than half full. Cover and hold lid down; pulse a few times before leaving on to blend. Puree in batches until smooth. Transfer salsa to a bowl and stir in vinegar.
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