It's easy enough to discern in desktop Macs when you need to do so.
True 'soft power' (called active power-control by Apple) needs a keyboard power-key, and there is no AC mains-power toggle-switch at the rear of the Mac. There may also be a soft-power (indicating) switch at the front of the Mac. (Most Macs from the Mac II series onwards)
Pseudo-soft power Macs have an AC mains-power toggle-switch at the rear of the Mac, but can respond to a keyboard power-key. (Colour Classics/P250 and P275, and many of the all-in-one LCs, Performas, and 5nnn PowerPC Macs)
Passive power-control Macs have only an AC mains-power toggle-switch at the rear of the Mac. The toggle-switch must be used even if there is a keyboard power-key. (All Compact AIOs from SE to Classic II. Macintosh to Plus don't use ADB keyboards at all.)
de
True 'soft power' (called active power-control by Apple) needs a keyboard power-key, and there is no AC mains-power toggle-switch at the rear of the Mac. There may also be a soft-power (indicating) switch at the front of the Mac. (Most Macs from the Mac II series onwards)
Pseudo-soft power Macs have an AC mains-power toggle-switch at the rear of the Mac, but can respond to a keyboard power-key. (Colour Classics/P250 and P275, and many of the all-in-one LCs, Performas, and 5nnn PowerPC Macs)
Passive power-control Macs have only an AC mains-power toggle-switch at the rear of the Mac. The toggle-switch must be used even if there is a keyboard power-key. (All Compact AIOs from SE to Classic II. Macintosh to Plus don't use ADB keyboards at all.)
de