I've just noticed that the "Schenectady & Margaretville" described duplicates your "Delaware & Eastern" entry, which makes sense since the former was a sub of the latter.
Two electric railways which I think may qualify, but which need more research, are:
BUFFALO, BATAVIA & ROCHESTER ELECTRIC.
This was incorporated in 1904 to build a heavy-rail fast interurban between these three places, with third-rail power. Actually it would have started at Williamsville, where it owned a little trolley line connecting to the Buffalo city streetcar system and at which passengers would have had to change.
What it managed was to build a small streetcar system at Batavia. However, it seems to have done a lot of preparation in the way of buying land and raising funds, and I suspect it did some ground-work as well. Although I haven't seen any evidence, if you look at the map you will see it was almost certain it would have wanted to use the abandoned "Buffalo, Corning & New York" grade and I wonder if it bought it.
BUFFALO, TONAWANDA & NIAGARA FALLS ELECTRIC.
When the "International Ry" was formed in 1902 to consolidate the electric lines between Buffalo and Niagara Falls, it inherited four competing lines between Buffalo and Tonawanda. This one was building on a dog-leg route bending to the west, and according to the contemporary topo map managed to build up Niagara St at Buffalo to Frog Island, and from downtown Tonawanda along Fletcher and Rogers to the end of Taylor St. The IR turned the former into a Buffalo streetcar line, and seems to have abandoned the latter fairly quickly. I suspect that work was in progress to fill the gap between the two segments in 1902, when the IR took over and abandoned further progress.
(Incidentally, the corresponding dog-leg route to the east, along Egger Rd, was the "Buffalo, North Main Street and Tonawanda Ry" and was junked in 1902, one of the earliest interurban abandonments.)