Comment by CamperBob2

A couple of good examples of (much) earlier switching supplies from Ken's site:

1) 1960s-era tech used in the Apollo Guidance Computer: https://www.righto.com/2019/08/reliable-after-50-years-apoll...

2) Mercury thyratons used in 1930s-era Teletype hardware: https://www.righto.com/2018/09/glowing-mercury-thyratrons-in...

Might be some other candidates as well, but those are a couple of the more interesting ones he's gone over.