Powering a radiator fan with 12V DC power supply
There are several possibilities:


The continuous current required by the fan is more than the continuous current rating of the power supply.
The short-time current required to start the fan is more than the short-time overload rating of the power supply.
The fan is started and stopped more frequently than the repetition rating for short-time overload of the fan.
The fan's bearings are failing causing the motor current to increase when the fan gets warm.


If the fan was taken from a vehicle that has a 12-volt electrical system, a 12-volt power supply that has an adequate current rating is what should be fine. A battery charger probably has an output of 15-volts or so. The vehicle may output 15 volts when the battery is being charged, so that should not harm the fan, but it will not make a good comparison for the power supply that has failed.

For re-purposing a motor, it is always helpful to have the means to measure the continuous motor current. Measuring the starting current is more difficult, but that would also be helpful.

If you have another power supply to try, it essential to know at least the current rating of that supply and compare it with the supply that has failed.