@Alex, You seem to be making the mistake of equating “linear == unregulated”, and equating “switch mode == regulated”.
A traditional supply with a big heavy mains transformer, can be very closely regulated - just stick a voltage regulator on the output, or even just a zener diode. Its voltage will be regulated, just not likely to be very efficient.
A switching supply is likely to be much more efficient, but there is nothing in the definition of “switch mode” to mandate that it is closely regulated.
There is nothing “pointless” about testing O/C voltages. Lots of devices consume only tiny currents, nano Amps if not micro Amps when idle or in “sleep mode” yet their supply decoupling capacitors will still be charged to the full voltage... Not a problem if they are designed for it, but a problem if they are not.
Moreover, my “open circuit” measurement was of course a little white lie as my DVM itself drew a small current so not really open circuit. I think input impedance is 10Mohm, iirc.