The Dow Jones Industrial Average surged nearly 550 points Wednesday as U.S. stocks extended a recent rebound, advancing as a congressional power divide eased worries about swift policy changes that could hurt large companies.

Uncertainty about the elections was one factor driving October’s stock-market rout, with some investors anxious that radical economic policy changes could hurt corporations benefiting from tax reform and an emphasis on deregulation. Democrats claiming a majority in the House of Representatives and Republicans…