The correct answer to this question is Mechanical -> electrical. There are many devices that can transform mechanical energy into electrical energy. The most known is a generator. Generators can come in various sizes and can be small to supply power to a flashlight or larger to supply energy to businesses and cities. The concept of a generator was discovered by 19th century inventory Michael Faraday.
They are important espeically during times of storm when traditional power may go out. for they are able to create electric energy. Other devices that can perform this transformation include a hall effect, an alternator, piezo electric, and triboelectric.