get continuity between the s-shaped swigglely lines?
NO!. Those should be
open-circuit both ways!
Well, that depends on whether it's in-circuit or not. In circuit, it
probably will show continuity both ways (with about two diode drops of
voltage developed), or possibly less if there's an isolation
However, SMPSUs are full of low-resistance components (the transformer
windings, current sense resistors (which may be < 1Ohm), etc. IMHO the
only way to reliably test components is out-of-circuit. I think I
mentioned that in another message.
transformer between it and the mains.
I have never seen an SMPSU with a mains isolation transformer. Yes, I
have seen PSUs that start with a mains transformer (giving, say, 20V),
and then use a switching regulator to bring that down to 5V (or
whatever), but I've never seen one with a 1:1 isolating transformer
(remmeber that 200V electrolytic, there is rectified mains in that PSU).