Stir together salt and sugar in a small bowl; sprinkle salt mixture evenly over short ribs. Place in an even layer on a wire rack set inside a large rimmed baking sheet. Let stand, uncovered, at room temperature for 1 hour, or refrigerate, uncovered, for up to 3 days. (If refrigerating, let stand at room temperature for 1 hour before proceeding with recipe.)

Preheat oven to 300°F. Heat oil in a large skillet over medium-high. Add half of the seasoned short ribs in even layer; cook, turning occasionally, until evenly browned, about 8 minutes per batch. Place seared short ribs in a large Dutch oven, and set aside; repeat process with remaining seasoned short ribs.

Whisk together 6 cups water, Shaoxing wine, and ¼ cup mushroom bouillon powder in a large bowl or measuring cup. Pour over short ribs in Dutch oven, ensuring short ribs are fully submerged and adding additional wine, if needed, to fully cover short ribs. Bring to a boil over high. Remove from heat, and place a piece of parchment paper directly on surface; cover with lid, and bake in preheated oven until tender, about 4 hours.

Using tongs, remove short ribs from Dutch oven, and place on a baking sheet. Pour braising liquid through a fine wire-mesh strainer placed over a large heatproof bowl; discard any solids. Measure out 2 ½ cups braising liquid; discard remaining braising liquid, or reserve for another use. Wipe Dutch oven clean. Whisk together 2 ½ cups braising liquid, strawberry jam, black vinegar, and remaining 1 ½ teaspoons mushroom bouillon powder in the same Dutch oven. Cook over medium-high, whisking occasionally, until sauce is thickened and reduced to about 3 cups, 20 to 30 minutes.

Add short ribs to sauce; cook over medium-high, turning occasionally, until short ribs are glazed and sauce is thick, shiny, and sticky, about 5 minutes. Serve short ribs with sauce.