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Two of the very most common terms dealing with current and voltage in devices are the power supply and uninterruptible power supply. Although they sound similar, these two devices are quite different from each other.


Uninterruptible Power Supply versus Power Supply: The Difference


A UPS offers protection from sudden power interruptions by instantly supplying energy from batteries so that the load never experiences an interruption and continues to support the load for a given amount of time which can range from minutes to hours.


A power supply unit supplies power to an electrical device such as a computer by converting AC to DC from the power utility.


This Article Deals with Power Supplies


AC-DC power supply typically takes the voltage from a wall outlet (mains supply) and uses a transformer to step up or step down the voltage to the desired voltage.


Power Supply Basics

The aim of a DC power supply is to provide the required level of DC power to the load using an AC supply at the input:

  1. PSU changes (in most cases reduces) the level of current supplied to a suitable level of current for driving the load circuit.
  2. It produces a DC supply from the main (or line) AC sine wave.
  3. It prevents any AC from appearing at the supply output.
  4. It will ensure that the output voltage is kept at a constant level, independent of changes in:
  5. Variation of the AC supply voltage at the supply input.
  6. The load current is drawn from the supply output.
  7. Temperature.

ac input image

What to Remember When Choosing a Power Supply Unit


DC Power Supply Specifications

When choosing any DC power supply, the suitability of a particular power supply for an application is determined by various attributes of the power supply listed in the power supply’s specification. Commonly specified attributes for a power supply include:

  • Input voltage type (AC or DC) and range:
    • The voltage and current are the two most important parameters quoted in volts and amps. Sometimes the output power in watts may be quoted.
  • The efficiency of power conversion
    • A benchmark for quality is the 80 Plus efficiency rating, which is a voluntary certification program for efficient energy use in power supply units for computers. This rating determines the efficiency of the power supply at converting AC power to DC power.
  • The amount of voltage and current it can supply to its load
  • How stable is the output voltage or current under varying line and load conditions
  • Operating and storage temperature ranges
    • Measured as a percentage or absolute voltage change per degree C.
    • Should be in the region of 0.02% / degree C or 2 mV / degree


The Packaging is Important:
  • A bench power supply: is a stand-alone desktop unit used in applications such as circuit tests and development.
  • Open frame power supplies have only a partial mechanical enclosure, sometimes consisting of only a mounting base; these are typically built into machinery or other equipment.
  • Rackmount power supplies are designed to be secured into standard electronic equipment racks.
  • An integrated power supply is one that shares a commonly printed circuit board with its load.
  • An external power supply, AC adapter or power brick, is a power supply located in the load’s AC power cord that plugs into a wall outlet; a wall wart is an external supply integrated with the outlet plug itself.

Power supplies are a fundamental component of many electronic devices and therefore used in a diverse range of applications such as:

  • Computer and computer peripheral power supply
  • Electric Vehicle power supply
  • Welding power supply
  • Aircraft power supply
  • Embedded electronics
  • AC adapter
    • Electronic devices have their DC converting rectifier built right into the device.
      • Computers
      • Stereos
      • Smaller electrical appliances
    • Medical equipment

Peninsula Technical Sales ( is an expert on power supplies and uninterruptible power supplies and can guide you in choosing the correct power supply or uninterruptible power supply.  Please call us at 650-965-3636 or Email us at  We are happy to answer all the questions.


Peninsula Technical Sales represents electronic equipment manufacturers and is proud to offer our services online and to the following cities and their surrounding areas: San Francisco, Santa Clara, San Jose, Fremont, Sacramento, Milpitas, and Santa Rosa.