Looking at the backs of my own machines, synthesizing from the above, and failing to refind the Apple kbase article, I suggest that it goes:

Macintosh, 128K, 512K, 512Ke: 120V or 240V.

Plus: probably 120V or 240V, since the 512Ke was so. (The 'Macintosh Minus' was released after the Macintosh Plus.) There is a separate 240-V (661-76214) power-sweep board available for Macintosh to Plus.

SE: same analogue board/power supply (661-0371/661-0370) as the SE/30, so ... ?

SE/30: autoranging, and saying so in red on a sticker behind the Mac.

Classic, Classic II: back to 120V (661-0597) or 240V (661-0599), an economy(?) measure.

IIcx, IIci and after: take autoranging for granted (661-0467 PSU with no special sticker), but 110-240V is in the moulded-in model spec. panel.

That leaves II and IIx unaccounted for, but likely to have been autoranging (661-0375 PSU).

However, contrary to that orderly(?) sequence is that the Portrait Display (1989) is autoranging, but the Multiple Scan 14 Display (1996) is 120V or 240V.

In short, one best reads what is on the back of the machine or device, or finds a Service Source manual.

de