I think EDDT's point was that shavers tend to work as expected when connected to the dedicated 'shaver' outlets. I suspect there must be a 50/60hz inverter on those for this to be the case.
BTW: Trivia point on electric clocks, the power companies don't actually hold 50/60 super accurately, can be a little fast as load goes down etc.
What they do is adjust the frequency so on average the clocks keep perfect time, using their own clock and an external standard.