Most diesel-electric trains are not hybrids, they have no batteries and therefore always get power from the single source, the diesel engine. There have been attempts to make them hybrid by putting a car in that contains a lot of batteries for say storing power down a mountain to use going back up the next mountain rather than converting the power to heat in the dynamic braking grid. My understanding is so far it is not worth the cost or complexity for the minimal savings.

Diesel-electric is actually less efficient than a mechanical coupling at steady speed due to double conversion losses which is about 80% efficient vs high 90's for gears through standard mechanical transmission. Trains use the an electric drivetrain because they need precise traction control with huge torque to get the train moving, a mechanical transmission with torque converters, clutches and gears would be difficult to route power and wear out too easily due to the low speed lugging. Once up to cruising speed however it would be more efficient.

This is why there are no hybrid semis or even diesel electric semi's, standard mechanical transmission are more efficient and hybrids only have significant gains in stop and go traffic where as for mostly highway travel the hybrid would normally disengage and simply be dead weight in a parallel hybrid or simply a efficiency drain in a series hybrid. This is also why most hybrid cars are not series, they mechanically couple the engine to wheel for efficiency once up to speed.

Planes again would have little gains from being a hybrid as they would spend most of their time at cruise running the combustion engine and a straight mechanical connection from engine to prop is much more efficient and lighter than any electric double conversion scheme.

Electric planes might make sense because there is no double conversion or engine in the plane itself, but you still have the issue of energy density with batteries.