I need to purchase a couple of small power transformers. I've always noticed that a lot of transformers have primary windings for 115V, 117V, 120V, and maybe even more. Some of them have all of the above in one single transformer, while some are labeled with just one as their primary voltage. Yet, they are sold as "mains voltage" to some other voltage. I totally understand why the secondary windings could be for any number of voltages, but the primary winding... I would think... wouldn't really change, right? Yet... it definitely seems to.
What am I missing?
What am I missing?