text: From 1927 on , the trophy was awarded to the champion of the American Division of the NHL , while the O'Brien Cup was presented to the Canadian Division champion , until 1938 , when , after the NHL reverted to a single division , the Wales Trophy was made the award for the overall regular season champion .
simplified: From 1927 â `` 28 onwards it was awarded to the champion of the NHL American Division while the O'Brien Trophy was awarded to the NHL Canadian Division . It was then repurposed to being the trophy for the overall regular season champion in the 1938-39 NHL season when the NHL reverted to a single division .