Many 220V switched mode power supplies are actually capable of doing 110V.
Have a look at
The 110/220V switch is a single pole switch which connects one of the bridge rectifier terminals (usually the neutral) to the mid point of two capacitors on the DC side of the rectifier.
This turns the bridge rectifier and the capacitors into a voltage doubler, and the rest of the circuit (from the input reservoir capacitor onwards) is left unchanged.
To find out if this applies to a PSU you need to reverse engineer a circuit diagram of the the AC input side of the PSU from the input terminals, past the EMC filters, then as far as the reservoir capacitor(s) (the fat thing(s) rated at about 350V or more).
If you find two spare PCB pads, with one pad connected to the incoming AC, and the other connected to the junction of two capacitors, then you've identified where to solder a link to turn the 220V PSU into a 110V one.
Note that some designs use two reservoir capacitors (as per the YT video above).
Other designs use smaller polyester capacitors to double the voltage, with a single capacitor doing the reservoir job.
For anyone wanting to go in the opposite direction (110V PSU on 220V supply), the solution is similar - reverse engineer to identify the link (if it exists), or the PCB track that does the same job, and then cut it, ensuring at least a 5mm gap between both ends (cut both ends of the link and remove, or if cutting a PCB track cut the track in two places about 5mm apart, and remove the intervening copper)
Usual "if you don't know what you are doing, ask an engineer" disclaimer applies - there's about 350V DC lurking on the capacitor and possibly on the transistor heatsink, enough to give you a belt if you aren't careful if the power is off, and enough to kill you if you are silly enough to turn the power on with the PSU opened up.
