"Lionchief engines cannot be run by a transformer handle, although Lionchief+ engines can"
To expand on this:
LC locos can run on a conventional loop that employs transformer voltage control, but the Lionel remote or universal must be used to control the LC loco. LC locos will function independently of the PS2/3 and conventional locos and will not respond to changes in transformer voltage setting.
Obviously if DCS is present, the PS2/3 locos will not respond to changes in the conventional transformer voltage either. So a lot depends on whether DCS is present. If the DCS signal is not present, the transformer voltage will affect only the Williams and PS2/3 locos.
If you have LC+ locos, when set to LC+, they will also not respond to the voltage control of the transformer, but to the Lionel remote that comes with the loco, or the universal remote. LC+ locos, as noted above, can function in conventional mode if you throw the switch on the loco to conventional.