I had a manager who received one of the first PS/2 PCs in our office. We had an agreement with IBM that they would send out someone to install all equipment (including PCs as they were very new to us). The manager the PS/2 was destined for decided that he could install the new box himself. He assembled the system (forgetting to plug in the mouse), fired up the PS/2 and was rewarded with the Windows desktop. When he went to do something he realised he had forgotten the mouse. This was one of the "new" PS/2 bus mice (previously all we had were serial mice). He went to the back of the running PS/2 and plugged the mouse into the appropriate PS/2 port. The PC immediately shut down. All efforts to revive the box failed.
He rapidly re-boxed the PS/2 taking great care to put everything back where it should be and waited for the IBM tech to turn up to install the PS/2.
When the IBM tech removed everything and set it up it failed to startup. The IBM tech declared the PS/2 DOA and arranged a new one. He later told us that it was a defective motherboard.
By all accounts plugging a mouse or keyboard into a running PS/2 could cause a spike that would destroy the motherboard because of the way the PS/2 bus was connected to the system.
To this day I still give that manager a hard time whenever he gets something new and decides to set it up himself (he is a friend of mine long retired)...