Isn't this what the former TPC400 unit provided for folks who wanted this level of power? Granted, 20 amps is a lot of power... but if you're just running loops without lots of complicated track configurations (i.e., where most derailments occur), the TPC400 may be your ticket. You may need to hunt for the TPC400's though, 'cause I don't think Lionel is offering them anymore.
David