21st Century Power Grid Act This bill requires the Department of Energy (DOE) to establish a program to provide financial assistance for projects designed to improve the resiliency, performance, or efficiency of the electric grid, while ensuring the provision of safe, secure, reliable, and affordable power. The projects must demonstrate (1) secure integration and management of energy resources, or (2) secure integration and interoperability of communications and information technologies related to the electric grid. Each project must include the development of a cybersecurity plan and a privacy effects analysis that evaluates the project in accordance with DOE's Voluntary Code of Conduct, commonly known as the DataGuard Energy Data Privacy Program. The projects may be designed to deploy a new product or technology that could be used by customers of an electric utility.