The letter almost cost Nvidia $400 million. In late August, the U.S. Commerce Department sent a notice to the American chipmaker ordering it to halt sales of its most important chip, the A100, to Chinese customers. Overnight, hundreds of millions of dollars in potential sales that quarter looked as if they might evaporate. The company’s stock price fell 6 percent, and Nvidia warned the drop in sales could even slow down the development of its next generation chip, the H100.  Like almos