So much for the Federal Reserve killing the US dollar. When Fed chair Jerome Powell signaled last month that rate hikes probably won't happen anytime soon, many experts thought that would hurt the dollar. Powell said the central bank needed to be "patient" and see what happens next for the US economy. Low interest rates usually go hand in hand with a weaker currency. Think of Japan and the yen during its lost decades of negative rates, deflation and a sluggish economy. But the US Dollar Index has rallied 1.5% against other currencies after the Fed's January 30 meeting. That has taken many by surprise. An increase of 1.5% may not sound like a lot, but it's actually a fairly dramatic move in the usually sleepy world of currencies. The dollar is now up slightly year-to-date. That could wind up being a problem for big US multinational companies.