There is Voltage, there is amperage and there is resistance.

We won't be talking about resistance.

Voltage and amperage are the two components of measuring the intensity of electricity.

When compared to a flowing river, voltage is likened to the pressure of the water as it moves down the river and amperage is likened to the quantity of water that is moving down the river every second.

Now then. Voltage and amperage. They are both important.

First of, lets address Watts.

Wattage is voltage multiplied by amperage.

If you have 240 volts and 10 amperage, coming from the wall, you have 240 X 10 = 2400 watts available from the power point.

If the USB ports of your machine are still USB 2.0, each has 5 volts coming out of it, at half an amperage.

Therefore the total wattage of a USB 2.0 port is 5 X 0.5 = 2.5 watts.

If you are provided the voltage and amperage, you can calculate the total wattage by multiplying the two.

If you are given the voltage and the wattage, you can calculate the amperage by dividing wattage by voltage.

If you are given the amperage and the wattage, you can find the voltage by dividing the wattage by the amperage.

There are different contexts in which these pieces of information are relevant.

For example, given a 5 volt 1 amperage battery, the context is, how much electricity, this battery/object outputs, yes outputs.

In case of a USB 2.0 port. Being 5 volt, 0.5 amp, it provides that electricity to a device connected to it.

Both of the cases above are identical in context.

The specific voltage and amperage is given to the device connected to it.

Our next example is a motor, an electric motor. It requires 24 voltage and 10 amperage.

The Context is different. The motor does not provide 24 voltage and 10 amperage to a connected device.

The specific voltage and amperage is taken from the device connected to it.

It requires 24 voltage and 10 amperage from the connected device (battery or power supply).

The two context for the voltage and amperage specification are, it is an output (as it is in the first two examples) or it is an input (as it is the case in the last example).

In this, we divide devices into devices that provide electricity and devices that require electricity.

Devices that require electricity, have limited tolerance for variability of the voltage they receive.

The above electric motor requires 24 voltage. A source of electricity needs to be 24 voltage. No less, no more. (What limited tolerance means varies from one device to another.)

Devices that require electricity, can work with any amount of amperage they receive, as long as it is above or equal to the amount required.

The above electrical motor requires 10 amperage. A source of electricity needs to provide at least 10 amperage. If it provides 100 amperage, that will not negatively impact the electric motor. If it provides 1000 amperage, that will not negatively affect the electric motor. If it provides a billion amperage, that will not negatively affect the electric motor. Amperage of the device providing the electricity has to be equal or greater than the electric motor requires. More than what is required will have no positive or negative effect.

So. When buying a power supply, you need to look for one that has the same voltage output and the same or larger amperage output. Plug the power supply in the wall. Plug the electric motor into the power supply and your motor will be spinning.