The voltage of your electrical system is actually irrelevant, as what matters is that you have a grounded outlet.
You can only plug in the Earthing equipment to an adaptor if you have a grounded outlet to plug the adaptor into. So, if you purchase an adaptor with a grounded port on it, it will not work unless it is plugging into a grounded wall outlet.
Also, please ensure any adaptor has metal inside the plug holes. Plastic will not conduct the Earth's energy.
Most international countries will require a Grounding Rod to be able to use the Earthing products.