I bought a 120 to 240vac power transformer, it didn't say step up or step down. My plan was to use it as a step up, after searching the internet I found the company (Jefferson electric) usually makes these as Machine Tool step down control transformers. The KVA rating I need is well within the limits so would this work as a step up ok? I see a lot of power converter boxes (transformers) sold on Ebay as either step up or step down, just where you hook the input determines which it is.

 

The KVA rating I need is well within the limits so would this work as a step up ok?

It will work either way, but if the turns ratio is designed to slightly increase the output voltage to allow for the winding resistance when used as a step-down, then the voltage will be slightly low when used as a step-up transformer.