Most straightforwardly: literally taking control over the electricity generation facilities. Less straightforwardly: bitcoin (and other cryptocurrency) miners. Even less straightforwardly: the same way the OpenAI et al. pay for their electricity, by selling the capabilities of its AI for interested parties to use.

With crypto.. that it makes on Polymarket-like ways, or creates its own content? Or blackmail humans? :-) I'm not entirely serious with my comment and do agree with you that there are lots of more immediate safety topics we should address before worrying about the AI becoming self-aware. That said, finding ways of accumulating valuable resources could be intermediate activities the AIs will attempt to do to complete it's 'goals' even when they're human-set!