Firstly, car battery chargers are expensive, in part, because they need to supply a lot of power. I'm sure the current requirements for the window motor are quite a bit less than what is needed to charge a battery. Furthermore battery chargers are usually higher voltage than 12V, and need to be to charge a battery to its actual fully-charged state, which IIRC is something like 13.2 V

I'd simply google search for a 12VDC power supply, and look for one that lists a maximum output current that exceeds the specified current draw of the window motor.

You might even be able to use a much smaller power supply to "trickle charge" rechargable batteries, and the batteries would be providing the power to the motor.

Secondly, you probably don't need two power supplies. The window motor probably wants +12 volts on its two leads to go up, and -12 volts on its leads to go down, which does make it seem that you'd need two supplies, however it is fairly easy to wire up a couple of relays to provide +12V and -12V to these wires from a single supply.

A year ago I made an automatic gate timer for a horse paddock, which locks the gate when it is closed, and then automatically unlocks it when a timer expires. That circuit used a power lock mechanism from a car door, and it required +12V to open and -12V to close, so I'm sure you can use a similar relay circuit to the one I used.

Indeed most car window motors are fed with a DPDT switch that connects the motor in the opposite polarities to drive it.

Most modern computer power supplies have a 12 volt output, and there are folks throwing away old computers every day. Determine your amperage requirement and find a power supply that meets the need.

For example, look at this article about using an ATX power supply (FYI - ATX is the type of computer power supply, not a brand)

. http://www.instructables.com/id/Convert-an-ATX-Power-Supply-Into-a-Regular-DC-Powe/

Bruce