Alternator #1 had failed en route to Tulsa, OK. Alternator #2 failed on the next flight to Davenport, IA. It was night with IFR conditions in Iowa. I diverted to Kansas City and spent the night. The next day alternator #1 was replaced. Alternator #2 was OK. I later learned that a single alternator cannot carry the full load of the plane including the deicing systems. The alternator master switch could not reset alternator #2 because its circuit breaker had been tripped. If I had reset the breaker, we could have flown on to Iowa.