Whisk soy sauce, hoisin sauce, sherry, black bean sauce, ginger, brown sugar, garlic, sesame oil, and five-spice powder together in a shallow glass dish. Add tenderloins; turn to evenly coat. Cover the dish with plastic wrap and marinate in the refrigerator for at least 2 hours or up to 24 hours.

Preheat the oven to 375 degrees F (190 degrees C).

While the oven preheats, remove tenderloins from the refrigerator. Remove tenderloins from marinade and shake off excess. Discard remaining marinade.

Bake in the preheated oven to desired doneness, 30 to 35 minutes. Let stand 10 minutes, then slice diagonally into thin slices.