Southeast Asia has been planning a unified electricity grid since 1997. Now, nearly 30 years later, its leaders are giving renewed impetus to the push to get energy flowing seamlessly across borders and seabeds. In Cebu earlier this month, leaders of the Association of Southeast Asian Nations put the power grid’s development high on their summit agenda, aiming to better insulate the region against the next big energy shock. But as regional governments try to turn the decades-long dream of an...