"I have had a shock from the pins of the 3 pin plug of my cylinder vacuum cleaner after simply using it and coiling up the lead."

That's from a capacitor fitted to suppress radio interference.
It's only a small value capacitor and though it might give you quite a surprise, it wouldn't kill you unless you already had something very wrong with you like a weak heart. It it was dangerous, they wouldn't be allowed to make it like that.

The electrolytic caps in a computer power supply have several thousand times the capacity of the suppressor in your vacuum cleaner.