NEW YORK—As the S&P advanced 0.9% the moment awestruck investors saw all the bills spread out in a dramatic fan, financial experts confirmed that the U.S. stock market rallied significantly Wednesday following the Federal Reserve chairman Jay Powell’s flamboyant display of a huge wad of cash. “Holy shit is that a fat stack, and all hundreds, too. Okay, this Fed chief guy must be loaded,” hedge fund manager Soren Westerman said as a self-assured Powell threw the roll of bills on a nearby Wall Street table, producing a deep thud so impressive the DOW rose 120 points in late trading and the Nasdaq Composite notched another 1.2%. “I mean, damn, if the chief of the Fed is throwing around hundy stacks like they’re nothing, the Fed itself has got to be doing well. Otherwise, why would he act like cash means nothing to him?” Prominent economists, however, have cautioned investors that Mr. Powell may have been pulling a fast one on everyone by putting his big bills on the outside.