U.S. stocks opened with big gains on Wednesday, as fresh stimulus from China's central bank as well as upbeat data on durable-goods orders boosted confidence. If the main benchmarks close at the levels they opened, it would be their biggest gains this year. The Dow Jones Industrial Average DJIA, -1.84% jumped 422 points, or 2.7%, to 16,077. The S&P 500 SPX, -1.15% opened 44 points, or 2.4% higher at 1,912. The Nasdaq Composite COMP, -0.13% began the day up 122 points, or 2.7% at 4,627.