Heat oven to 275°F. Heat oil in Dutch oven on medium-high. Season pork with 2 teaspoons salt and 2 tablespoons five-spice powder and cook, turning occasionally, until browned on all sides, 10 to 12 minutes; transfer to bowl and discard all but 2 tablespoons fat.
Return pot to medium, add garlic and onion and cook, stirring occasionally, 6 minutes. Stir in maple syrup, soy sauce, vinegar, lime halves and remaining 2 tablespoons five-spice powder; bring to a simmer.
Return pork to pot, cover, transfer to oven and cook, turning after 2 hours (adjust oven temp to keep the liquid at a slow simmer), until meat is tender, 4 hours. Uncover, return to oven and cook until deep golden brown, 30 minutes.
Remove pork from liquid, discard lime halves and skim off and discard fat. Simmer liquid until slightly thickened, 15 min. Stir in lime juice. Shred pork into chunks, discarding fat; fold into sauce. Serve with rice, scallions, chiles and limes.
