Older speakers like that use always on transformers, constantly wasting energy to keep the core energized. You’re correct those cannot be made any more, they must use efficient switch mode supplies.

+1 on this idea, going to toss in my recommendation for an AMD 5600g second hand. Its basically a laptop CPU with built in GPU that handles my jellyfin transcoding without issue and has a super low idle power rating if you pair it with a quality, small PSU.