Actually, he would.
When you deal with transformers that are big enough (just the one of your microwave is big enough for that) once unplugged it can still deliver a strong zap or two (which can easily be lethal as it is a zap with less voltage and more amperage) before being discharged.
You really shouldn't mess with those.
This can also happen with a battery or anything holding electricity in fact, with of course different range of dangerousnesses, but Sans here don't really have room for error.
Actually, if you unplug your microwave and take the transformer and start messing with it right away, there's a good change you'll die.
It can still deliver one or two zaps before being discharged, and a zap having less voltage and more amperage is way more lethal (like, really).
You can also receive a zap from batteries this way, or anything holding electricity, with zaps that are more and less dangerous.
But here Sans doesn't really have room for error wherever or not this thing from the printer is more or less powerful than the transformer of a microwave.