Early switched mode power supplies.

[Nick]

From the television engineers point of view the switched mode power supply employed in the 1969 BRC 3000 TV chassis was the first time such technology was introduced in domestic TV sets.
However, I'm sure SMPSUs were used in the electronics industry much earlier than 1969.  Patents were taken out in the late 1950s.

Interesting article: https://www.xppower.com/resources/blog/h...plies-smps