Found a dimmer switch rated 250V AC 40 - 250W
Can this be used?
It will be an experiment with i'd estimate 60% chance of success.
It'll either work fine or wreck the dimmer, so if it's one you already have and don't mind sacrificing...
I have an extension cord with a lamp dimmer & receptacle in a box at one end just for experiments like this. One side of receptacle gets full voltage, other side is through dimmer. In US that's easy because our receptacles provide for separate feeds.
Try it with a lamp first . Then set it to minimum , plug in the charger and bring voltage up slowly while listening for unusual humming in your transformer.
Asymmetry in the dimmer output will make the transformer hum and run hot but it should self-announce by those symptoms..
You might feel a little line frequency vibration in your motor but that's expected.
Keep this thing safe. PF is wary about inexperienced people working with line voltage.
Be sure you put the dimmer and receptacle in an outlet box and all connections are safe from tiny fingers in your household that are curious...
Your work in post #29 looks pretty good so i dont mind suggesting you give it a try.
I think over there you have fused appliance cords - one of those sounds like a good safety feature. I don't like 240 volts , the sparks are too big for me.......