In a 3- to 4-quart pan, combine ketchup, orange juice, raisins, brown sugar, Worcestershire, vinegar, soy sauce, ginger, garlic, onion powder, tamarind concentrate, and chili sauce. Bring to a simmer over medium-low heat, then reduce heat and barely simmer (a few bubbles breaking on surface), stirring occasionally, until sauce is thick, glossy, and dark brown, about 2 hours. In a blender or with a handheld blender, pulse until almost smooth. If sauce is too thick, thin with a little more orange juice. Let cool; serve or chill airtight up to 1 month.
Nutritional analysis per 1/4 cup.