If the no-load current at 10 volts is 0.5 amps, then at 5v it will be 0.25a and the motor will spin at half the speed.

If you try to run four motors at 5v, you'll need 1a.

As your supply is only rated for 0.5a, it could do one of two things. It could supply 1a and overheat, or you might find it's voltage drops.

Also, if you apply any load to the motor, it will draw a lot more power. Even during the second or so it takes to spin up, it will be drawing more than it's no-load power. So while you might be able to get one motor to run, you won't be able to get any useful work out of it.

I don't think it's a good idea to try to run a 150W motor from a 2.5W power supply - and trying to run 4 motors will definitely overload the power supply.

You would be better to use the power supply for a laptop, or from an old desktop computer case.

The no-load current doesn't change much with voltage.

If you try to run four motors at 5v, you'll need a 2amp supply.

As your supply is only rated for 0.5a, it could do one of two things. It could supply 2a and overheat, or you might find it's voltage drops.

Also, if you apply any load to the motor, it will draw a lot more power. Even during the second or so it takes to spin up, it will be drawing more than it's no-load power. So while you might be able to get one motor to run, you won't be able to get any useful work out of it.

I don't think it's a good idea to try to run a 150W motor from a 2.5W power supply - and trying to run 4 motors will definitely overload the power supply.

You would be better to use the power supply for a laptop, or from an old desktop computer case.