Heat the oil in a large skillet over high heat. Sprinkle the salt and pepper evenly over the pork chops and add to the skillet.
Brown the chops on both sides, adding a few at a time, being careful not to crowd the pan, and transfer to the insert of a 5- to 7-quart slow cooker.
Melt the butter in the skillet over medium-high heat. Add the onions and sautÃ© until they begin to soften, about 5 minutes. Add the remaining ingredients and scrape up any browned bits from the bottom of the pan. Transfer the contents of the skillet to the slow-cooker insert.
Cover and cook on high for 3 to 4 hours or on low for 6 to 7 hours. Skim off any fat from the top of the sauce. Serve from the cooker set on warm.