Question Finding Motors

There may be second hand powered wheelchair motors available locally, if you hunt around.

You could order from China.

You can, but keep in mind wiper motors are not that powerful so they favor a design with a lot of inherent leverage and low mass.

Keep in mind that wiper motors also need ground isolation: https://www.xsimulator.net/community/faq/wiper-motor-mandatory-ground-isolation.25/

The PSU(s) plug into mains power.

Your house power outlets.

Which wall plug depends on where you are in the world, and what PSU is used can also affect how a wall plug is connected to it, but for example here is Meanwell PSU plug connection: https://www.soundimports.eu/en/blogs/blog/9-how-to-connect-the-mean-well-power-supply-to-an/

If you are not comfortable or confident with mains power then consult an electrician, as mains power can kill.

Where are you located in the world?

You will need a power plug and cord for whatever applies in your part of the world.

That gets wired into the PSU, which changes whatever the voltage is that is used for appliances in your part of the world to 12v.

I already did with the previous link: https://www.soundimports.eu/en/blogs/blog/9-how-to-connect-the-mean-well-power-supply-to-an/

But as per my warning, if you are not confident with electrical wiring get an electrician to do it, it is a 30 second job to wire a mains plug to a 12v PSU, but it is important to ensure it is done right and even after that treated with care, as mains power can kill.