First off, are you running strictly TMCC/Legacy command mode? If so, I recommend the Lionel PowerHouse 180 bricks, great circuit breaker and a true 180 watts of power in a small package.
If you're wanting to run conventional mode as well, consider the PowerHouse 180 paired with the Lionel Legacy PowerMaster, that will allow you to run conventional locomotives from the CAB2 remote.
You can use the original ZW, however for any locomotive with electronics, I recommend adding a modern circuit breaker between the ZW and the track.