Adding a switchable power supply

[DustyK47]

I have a friend that wants me to add a switchable power supply to his boombox.

Right now it's only able to be powered (besides batteries) with North American 120V AC.

How difficult would it be to do a modification like this; as I've never done anything like this before.

 

[Superduper]

Easiest to just switch the power transformer to suitable voltage version for the local country mains power.