The ISB is an autoformer.
The term autoformer is not in my vocabulary I guess. The ISB does have a transformer that is controlled by some electronic stuff. But it is a voltage regulator meaning it adjusts incoming voltage so the outgoing voltage is acceptable. I do not know of anywhere outside of Mexico to get one. Ask and maybe someone will bring you one. You can get an ISB almost anywhere in Mexico but you probably have to ask and bring all the info you can find online with you to any ferreteria and if they do not have one it can be ordered. No need for more than the 4000 in Mexico. Should cost less than $250US. Go to the website I posted above to learn about them. I know there are others but this is the only one I have personal experience with as well as knowing many others that have them.