Good intention trying to help people,
but it is more reasonable to simply install a new circuit with two hot wires + earth.
--> 220V outlet.
Yes, much better to add 240v point.
A couple of reasons why you need 240v is ,one, you need more power (240v provides double power at same current) or, two, more efficiency (PSU at 240 more efficient than 120).
But if you use a step up transformer, you are still 120V at the wall, hence no increase in power as your current limit stays same. And losses in step up transfer would negate efficiency gains (I think).