PHILADELPHIA—Ninety-eight years ago, the nation’s largest power grid operator was founded here by utilities serving Pennsylvania and New Jersey. Glenn Youngkin blame PJM for delays in approving new power projects, creating a bottleneck that is making the situation worse. “There’s an element of responsibility on both sides,” he said, meaning the states and PJM. What’s not clear is whether, or how, states leaving PJM would lead to a more affordable or reliable system. This restructuring meant that regulated utilities were limited to providing the delivery of electricity, while independent power producers would build and operate power plants.