Yes the transformers work on demand.
Originally Posted by donv
I can tell you this about going the other way. I bought a Casio Keyboard at a yard sale for my grandaughter but it didn't have a power supply. I had an old one that was the right voltage, but the amperage was about 20% of what it required. After about an hour, it killed the keyboard. That was the verdict from the repair shop.
As far as the keyboard failure. Some devices use DC transformers, some use a reduced
AC voltage. It would be easy to miss one little letter when trying to find a replacement.