This might be a long shot, since I feel like it has details you would have thought more prominent than energy concerns, but could this be Highlander: The Animated Series?
The story unfolds on post-apocalyptic Earth, after a meteorite collision nearly wipes out all human civilization after setting off nuclear weapons. Following this catastrophe, Connor MacLeod (the protagonist of the original film) and the other Immortals forswear the Game of fighting each other until only one Immortal remains to win the Prize. Instead, the Immortals swear to preserve human knowledge and help humanity. They cast away their swords and call themselves Jettators (from the French jette, "thrown away".)
But one Immortal, Kortan, refuses to swear the oath, he still seeks the Prize and now wishes to dominate the world. Connor challenges Kortan to a duel and is defeated and killed, as any Immortal who breaks the oath is destined to die. However, with Connor's death comes the prophecy of the rise of a new Immortal, unbound by the oath, who will defeat Kortan. Uncontested by the Jettators and nigh-unkillable by mortals, Kortan establishes an empire controlling most of the planet, which he rules from his fortress Mogonda.
As with the original movies, the central conceit is immortals battling it out with swords, but another recurring concern is powering society, with certain immortals hording the secrets of hydroelectric, or nuclear, power. And, as noted in the summary, it is a post-apocalyptic Earth caused by a meteorite collision, and it has warlords.
Intro and Credits
I found this series by searching for cartoon series asteroid "nuclear power" stops working. I have not personally watched it.