This is the Gilbert lettered version of the 22033 25 watt transformer that was included in the six panel sets. It has two output terminals and no circuit breaker.
This is the All Aboard lettered version of the 22033 transformer.
This is the 22034 50 watt transformer that was included in the eight and twelve panel sets. It has three output terminals and a circuit breaker and has the American Flyer lettering.
This is the All Aboard lettered version of the 22034.
Several of the collectors guides list the 22034 as a 110 watt transformer. While it is possible that a 110 watt transformer was included in the later 12 panel sets it is unlikely that it was a 22034. Some of the early six panel sets are reported to have a plastic case 22020 25 watt transformer that was used in the smaller Pikemaster sets previous to All Aboard. A good transformer to use with an All Aboard set (especially if you have the whistle panel) is a 15B 110 watt transformer. It has enough power to keep the train running smoothly and not slow down when you blow the whistle.
A note on safety: Due to the sheet metal construction of the 22033 and 22034 they can become extremely hot during use. Care should be taken to prevent short circuits when using the 22033 as it has no circuit breaker protection.