Which power cable should I use for a Macintosh 128K (upgraded to a Plus)
If it needs 110v then you need a power transformer, not just a kettle plug.
The plug known as a kettle plug often isn't one…
See the list of power couplers on WIkipedia - https://en.wikipedia.org/wiki/IEC_60320#Appliance_couplers - a 'kettle plug' is actually a high-temperature [C15] version of the more common IEC C13 plug.
You can buy IEC 13s just about anywhere - &amp; many people have spares from old computers etc still kicking around in drawers.
The C15 has a notch to prevent plugging a 'low temperature' C13 into it. Plugging the other way, a high temp C15 into a low temp C14 appliance is no issue.
Your issue isn't the plug, it's the voltage.
If you plug a 110v Mac into a 240v supply, you will kill it, stone dead.
If you can get a photo of the appliance rating sticker on the back, then we can be more certain.
Modern computing/electronics has universal voltage, anything from 100v to 250v would be fine. Older devices may need specific voltages, with only perhaps 10% tolerance.