Notably, the electric service lines that you see throughout this photo (telephone circuits were strung on the tall poles in the background) are pretty early and appear to be typical of pre-1900 construction. Distribution transformers are within view, mounted lower. In the early days a transformer typically fed one or two customers along a street. This became expensive owing to higher transformer-core line losses experienced. By 1910, the utility industry became well aware of this and transformer manufacturers began to build higher-capacity units that would serve at least several nearby customers along a street, eliminating the accumulated energy losses of transformers serving one or two customers at a time in a neighborhood.

PS...Nice, graceful use of insulator brackets upon the pole in the foreground :-)