[danby]

As I understand it the issue is that when the old c64 power supplies failed the 12v line would go overvoltage and fry your computer. The amiga power supplies are designed differently and don't have this "feature".

Though it is often worth replacing the original amiga power supplies as the capacitors are often shot by this point

[laubzega]

There is no 12V input to C64, just 5VDC and 9VAC. You are thinking about 5V supply, which indeed fried many computers when the PSU failed and ramped the voltage up.