All Apple laptops and portable gadgets (and
Mac Mini and
Mac Mini Server too) run 110-240 V. All those are made portable, as people
travel - and it's not worth the hassle to save $ 2 (or whatever the small difference might be for having a less wide range of voltage) in the manufacturing, if it would bring extra hassle and cost to the users - plus a lot of pain and unhappiness in the millions of cases one would just plug in the device without thinking.
So skip the voltage converter. All you need is a plain adapter - I would recommend of the "world adapter" type, such as
this. Look for one in a store that sells travel gadgets, or at airports etc. You may have to pay $ 10-20 for one adapter, but one is all you need (for one device) anywhere in the world. I've had to live with the pain of three kinds of plugs for many years: UK plugs in the house, or UK plugs expected. Most electronic gadgets with US plugs as they were and are not bought in UK. Some devices with Euro plugs, and then the joys of the three kinds of plugs used in all those 3 different places. No more of those one conversion only, and where you need 10 plugs to cover yourself. Just one, and it will last for years.
When traveling, I pack
two of those in my luggage if I go somewhere where I need one. That way I can use one and my other half can use one.
And in doubt for any model of Apple product whether it will run in some other voltage: check the website. The supported voltage is
always listed in the tech specs.
The voltage is one of the things why it doesn't really matter whether you buy your Apple laptop, iPad, or iPod in New York, Stockholm, London, Kuala Lumpur or Beijing. It will work anywhere. If you are for a long time somewhere where the plugs are different, you can usually just get the power cable (that attaches to the adapter) and replace that to eliminate the adapter.
So that could explain this message.