Before the 2008 financial crisis, US power trading was a thriving, multibillion-dollar business for a handful of major Wall Street and European banks. But in the past few years, those banks have sharply curtailed their presence in US electricity amid regulatory pressure and a broad tendency to scale back risk, according to market participants. Meanwhile, scores of their power traders have quit their jobs and gone to work for hedge funds or trading houses, where the regulation is looser and