Hi Chris
Are these Canadian 19 set power units ?
This article may be helpful
https://www.cool386.com/vibservice/vibservice.html
With vibrators, the contact points become oxidised after a period of storage. You can try to jump-start the vibrator by briefly applying a higher voltage . The points tend to self clean once the vibration action starts.
Another possibility is that the power supplies may need external switching. Are these power supplies you are testing connected to a radio set ?