Power supplies are devices that supply energy or electricity to an output load. It should be noted that the term is usually applied to electrical energy supplies.

The term power supplies can also be used in reference to secondary sources as well. These might include such things as: the conversion of one form of electrical power to another form. An example of this might be converting 120 or 240 volt AC supplied by a utility company to a lower voltage DC for electronic devices.

Power supplies might come from the local power company but they might also come from such things as batteries and other types of chemical fuel cells. Solar power is another example of power supplies that are coming of age. In the industrial area, generators and alternators are also power supplies.

Low voltage, low power DC power supply units are commonly integrated with the devices they supply, such as computers and household electronics. This includes devices that are small, such as wristwatches and mini-cameras.

While there are many sources of power supplies and many ways to deliver that power to a device, one thing that has been a problem for all power supplies is the limited amount of power that they can deliver to a device and the amount of time that they can do so.

Most power supplies require either re-charging or refueling at some level of distribution. Another issue that most power supplies have to address is stability. In other words, how stable is their output voltage or current under varying load conditions, and whether they provide continuous power or pulses.

In most cases, the stable regulation of power supplies is done by incorporating circuitry as a mean to tightly control the output voltage and/or current of the power supply to a specific value. This specific voltage value is closely maintained despite variations in the load presented to the power supply's output, or any reasonable voltage variation at the power supply's input. This kind of regulation is usually referred to as a "stabilized" power supply.

As technology advances and newer forms of power supplies are developed the issues of voltage stability should lessen or become less of a worry to consumers. Many consumer devices such as cell phones and audio players come with highly developed power supplies and re-chargers. Power supplies and re-chargers have never been as popular as they are now and this trend should continue for years to come.