Found hiding in a cupboard: the original power brick for the previous MBA: one of the five spring-loaded poles in the L-shaped Magsafe 1 tip was stuck down, unable to complete the circuit when in "cable behind" the laptop, only worked in "cable beside" orientation, which then prevented use of the adjacent USB port. I had to replace that adaptor.
But the newer MBA has the Magsafe 2 connection & $12 will get me a Magsafe 1 to Magsafe 2 adaptor, I'd be able to use the old dodgy Magsafe 1 tip on the new MBA effectively because the adaptor can be reversed, uncovering the USB port.