Apple - How to fix a frayed cable on a MagSafe Power Adapter?

Sugru - not cheap, but very good.

Goes on like Plasticene/Silly Putty, dries like rubberised plastic. Flexible & waterproof, lots of different colours.

Eventually there will be very light electricity shocks, I fixed all my cables with this tape it is very strong an the with ones are more esthetics for mac white cable.

It's called RESCUE TAPE Self-Fusing Silicone Tape ~ WHITE. I got mine from Amazon but there might be other places or similar tapes.