Powell is scheduled to address the US central bank's policy framework review, and investors are focused on whether he will hint at shifting the Fed's inflation target to an average.
The Fed is thought to be still finalizing details of its review, however, with an announcement expected at its September meeting.
The greenback took a hit after data on Tuesday showed U.S. consumer confidence tumbled to the lowest in more than six years due to concern about the coronavirus-induced job losses.
Sentiment for the greenback has improved somewhat due to supportive data on business activity and home sales, but there are still concerns that additional monetary easing may be necessary to keep economic growth on track.