Season chops with salt and pepper and brown in oil in a skillet for 2 minutes per side in 2 batches. Place fennel and onion in a 6-quart slow cooker and arrange chops on top.
Pour cider and broth around the chops, add sage and cover. Cook on low for 5 hours.
Add apple wedges around the pork, cover again and cook for 1 more hour until apples and chops are tender; pork must be at least 145°F and marbled blade chops generally soften near 190°F.
Lift chops and apples to a platter and rest the pork for at least 3 minutes. Transfer fennel, onion and liquid to a saucepan, skim excess fat and simmer for 5 minutes.
Mix cornstarch with cold water, stir into the sauce for 2 minutes until lightly thickened and add vinegar. Spoon the cider sauce and vegetables around the chops and apples.