Rochester NY had DC in the core city (inside the Inner Loop) until 1965. AC was also available, and many buildings had both systems. The DC was generated by Court St Dam on the Genesee river, owned and operated by NY State DOT. The generators and wiring were pulled from the dam in 1980, and the State paid a man to stand there and make sure everything was smashed and not rebuildable. Your tax dollars at work!
50 and 25hz systems also existed all over the country into the 50s. Churchville NY operated a 25hz system generating power from the falls in Black Creek and when their village municipal system tied into the grid from Niagra Falls, Churchville installed a rotary converter to change 60hz to 25hz power. The 25hz was discontinued around 1955 when the converter let all its smoke out and it became aparent switching the system to 60hz was more cost effective.
In the Rochester area the Interurban trains did a lot more to prove the transmission efficiency of AC over DC than all the professors in the world could have.
Many industrial plants and even downtown buildings generated their own electricity into the 1930s, when the PoCo, RG&E proved they could sell steam plant operators electricity cheaper than they could make their own. Only Eastman Kodak continues to burn coal and make their own electricity. Kodak can still make it cheaper due to economy of scale.