Using a sharp knife, trim excess fat from briskets, leaving only a thin layer of fat. Lightly season briskets with salt. Heat oil in large All-Clad Fry Pan over high heat. One at a time, add brisket and cook, turning once, until browned, about 8 minutes. Transfer to a platter. Season briskets with chili powder. Pour off all but 2 tablespoons fat from fry pan and reduce heat to medium. Add onions and garlic then cook, stirring often, until softened, about 5 minutes. Stir in chili sauce and beer; remove from heat.
Stack briskets in ceramic insert of the All-Clad Electric Slow Cooker. Pour in chili sauce mixture. Cover and cook on High until fork-tender, 7 to 8 hours.
Transfer briskets to platter; tent with foil to keep warm and let stand 20 minutes before carving. Strain sauce through sieve over bowl; reserve onions. Skim off and discard fat from sauce (use a gravy separator, if you wish.) Pour sauce into fry pan; boil until reduced by half, about 15 minutes. Stir in onions. Slice meat across the grain. Moisten sliced meat with some sauce. Serve, with remaining sauce served on the side. Makes 8-12 servings.
Adapted for the All-Clad 6.5-Quart Electric Slow Cooker with Ceramic Insert from The Slow Cooker Ready and Waiting Cookbook by Rick Rodgers (William Morrow.)