Contemplating how to power custom-built gear from the mains safely, and within the regs. So if I buy a 'bench power supply', I can connect the LVDC output to more or less anything, including a bare breadboard that I'm working on. But AFAIUI, that doesn't apply to a plugpack, which requires anything it powers to be 'approved double insulated' (see (*) following). So what's the characteristic of the bench supply that allows it to be used in this way?
(*) I was curious about how plugpack outputs go in terms of input-output leakage, so I checked the voltage between the output and local ground, for a couple of relatively new 9VDC SMPS units. Both of them showed open circuit voltage of > 90VAC, and a short circuit current to ground of around 100 uA. Not close to dangerous current level, but enough for a significant tingle, and enough to discourage use as a general supply around the workbench.