Put the pork in a large non-reactive bowl and toss it well with the salt and set it to the side
Remove the stems and seeds from the peppers. Place the cleaned peppers in a small pot and cover with about 3 inches of water. Bring the peppers to a simmer and cook for about 10 minutes. The peppers should be tender and plump. Drain the peppers
In a blender or food processor add the cooked peppers and all of the ingredients for the adobo. Puree into a smooth thick paste. If you need, add a splash of water to the mixture if its too thick. Add the puree to the bowl of pork cubes and mix well. Cover with plastic wrap and refrigerate for 2 to 4 hours.
Wipe off as much adobo as possible from the pork, while reserving the adobo for cooking. Place a heavy bottomed pot over medium heat and add the oil. When the oil is nice and hot (it should be shimmering), add the pork and cook until it is nicely browned on all sides (about 7-10 minutes). Add the reserved adobo, stock and onions. Cover the pot, reduce the heat to medium low and simmer for about 1.5 hours or until the meat is tender enough to easily shred and the liquid has reduced by half. Check for taste and season with salt, pepper and vinegar if needed.