I have been worried about this too. 
I'm thinking about getting this one https://www.amazon.com/Converter-toroidal-transformer-protection-continous/dp/B01NCU984W/ref=sr_1_17?ie=UTF8&qid=1510330262&sr=8-17&keywords=120v+to+220v+converter or this one https://www.amazon.com/Rockstone-Power-Voltage-Transformer-Converter/dp/B00CLYMMCC/ref=sr_1_19_sspa?ie=UTF8&qid=1510330262&sr=8-19-spons&keywords=120v+to+220v+converter&psc=1, not sure if anybody here used it or not?
I'm thinking about getting this one https://www.amazon.com/Converter-toroidal-transformer-protection-continous/dp/B01NCU984W/ref=sr_1_17?ie=UTF8&qid=1510330262&sr=8-17&keywords=120v+to+220v+converter or this one https://www.amazon.com/Rockstone-Power-Voltage-Transformer-Converter/dp/B00CLYMMCC/ref=sr_1_19_sspa?ie=UTF8&qid=1510330262&sr=8-19-spons&keywords=120v+to+220v+converter&psc=1, not sure if anybody here used it or not?
uhm I am as clueless as you guys but just wanted you to know that a step-up transformer is going to use more electric and add to your bill. From what I can see you should be able to get 1200W at the wall which is enough to power the antminers? I saw someone on youtube say his D3 was only using 1000 watts... But of course please do your own research and let us all know what you figure out. Thanks!