Hi there fiddler!,
Welcome to ECN. [Linked Image]
Regarding your question on a step-down Transformer, I suppose you could use a voltage stabiliser on the output, but finding a suitable type for that level of voltage, would be a different story.
For safety reasons the UPS should be plugged into a Grounded outlet.
As far as grounding the secondary side of the Transformer goes, unless anyone else here says otherwise, I'd advise against it.
Hope this helps. [Linked Image]