How do I convert a 240v outlet to 120v?
Simply so, can you turn a 110 outlet into a 220v?
Converting a 110-volt outlet to a 220-volt outlet requires extensive rewiring and most building codes would require inspection. There is an alternative available: Use a voltage step-up converter.
Likewise, can I use 125v outlet in place of 250v?
You have to mach the plug and receptacle to the voltage and amperage of the device. If it's 110-120V, use the 125V. If it's 208-240V, use the 250V. If heat dissipation is an issue, you have a design problem with the utilization equipment.
"It is both an adapter and step-down converter" - by Grace S. As an adapter, it comes with the usual US, UK, Europe and AUST prongs. As a converter, it can convert 220V (Europe, China, etc) to 110v, not the other way around though. There is a switch to select the adapter or converter mode.