Which decades are electricity historians often pointing to for the formalization of the electric utility industry?

The 1890s and early 1900s

While the invention and initial demonstration of centralized power occurred in the early 1880s, electricity historians generally mark the period spanning the 1890s through the early 1900s as the era when the electric utility industry truly began to formalize its structure and operations. This period involved shifting focus from pure invention to large-scale construction and the integration of AC technology into a viable distribution network. Key activities during this time included the standardization of voltage levels and frequency (like 60 Hz), the physical expansion of transmission lines between 1900 and 1920, and the consolidation of small, competing local power companies into larger corporations serving broader territories.