My absolute favorite! The "Krokodil/Crocodile" was introduced in 1919. Some are still in service.
About electrification, in 1928 55% of the 2900 km of SBB/CFF railway were electrified, 90% in 1946... (no coal in Switzerland). The dam of Ritom above Airolo, was build in 1920 to power the newly electrified Gothard line.

Hydropower is not always as clean as we can imagine. It's partly recycled french nuclear energy: at night, water is pumped up in the dam using cheap electricity and sold back during the day.