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 retaining control of the Senate soothed some of those fears, analysts said, sparking a broad-based market rally. Twenty-nine of the 30 Dow industrial stocks climbed, putting the blue-chip index about 2.5% off its October record. All 11 S&P 500 sectors posted gains, moving the benchmark roughly 4% off its record. Both indexes have risen in six of the past seven sessions, a quick turnaround from a brutal selloff that left the S&P 500 and Dow teetering on the edge of correction territory two weeks ago. While some sectors directly affected by Tuesday’s results such as health care led the indexes higher, a rally in recently battered technology and internet stocks was another sign of rejuvenated investor confidence.