Archives For Power Supply

External Power Supplies

eiodotcom —  October 3, 2012 — Leave a comment

Today’s EIO post is on external power supplies.



External Power Supplies 101


External power supplies are devices that convert ac power from a wall outlet into lower voltage dc or ac power to be used directly by electronic circuits. External power supplies come in a separate physical enclosure than the end-use product, and usually provide power to the device directly through a separate cord and plug. External power supplies are used to power a variety of electronic devices, including: laptop computers, printers, cordless phones, cell phones, etc.


External power supplies are used both with equipment with no other source of power, and with battery-powered equipment, where the supply both charges the battery and powers the equipment when plugged in. One of the benefits of using an external, rather than internal power supply is it increases the portability of a device, by avoiding the need of internal power components. Use of an external power supply allows portability of battery-powered equipment without the added bulk of internal power components and makes it unnecessary to produce equipment for use only with a specified power source.


Benefits of Using an External Power Supply

Safety — External power adapters can free product designers from worrying about some safety issues. Much of this style of equipment uses only voltages low enough not to be a safety hazard internally, although the power supply must out of necessity use dangerous mains voltage. If an external power supply is used (usually via a power connector, often of coaxial type), the equipment need not be designed with concern for hazardous voltages inside the enclosure. This is particularly relevant for equipment with lightweight cases which may break and expose internal electrical parts.

Heat reduction — Heat reduces reliability and longevity of electronic components, and can cause sensitive circuits to become inaccurate or malfunction. A separate power supply removes a source of heat from the apparatus.

Electrical noise reduction — Because radiated electrical noise falls off with the square of the distance, it is to the manufacturer’s advantage to convert potentially noisy AC line power or automotive power to “clean”, filtered DC in an external adapter, at a safe distance from noise-sensitive circuitry.

Weight and size reduction — When most power adapters featured simple mains-frequency transformer-based designs, they were quite heavy and large, and added considerably to the weight and bulk of devices designed to be lightweight. Even modern power supplies are relatively heavy compared to other circuitry. Removing power components from equipment powered by rechargeable batteries reduces the weight and size which must be carried, though use of other rechargeable batteries like sealed lead-acid batteries can questionably put more weight on the equipment.

Ease of replacement — Power supplies are more prone to failure than other circuitry due to their exposure to power spikes and their internal generation of waste heat. External power supplies can be replaced quickly by a user without the need to have the powered device repaired.

Configuration versatility — Externally powered electronic products can be used with different power sources as needed (e.g. 120VAC, 240VAC, 12VDC, or external battery pack), for convenient use in the field, or when traveling.

Some of Our Products  (To see all power supply products, click here)





Brand Velleman
Supply Voltage 100 ~ 240V AC
Power 36W
Efficiency >=70%
Selectable Outputs 5 to 24V DC in steps of 1V (from 4.3 to 1.5A)
Output Plugs 2.5mm mono, 3.5mm mono, 1.0×3.0mm, 1.35×3.5mm, 1.7×4.0mm, 2.1×5.0mm, 2.5×5.5mm, 1.5×5.5mm
Dimensions 3.5″ x 1.8″ x 1.2″
  • with 8 detachable DC plugs
  • for notebook computers & personal digital electronic devices
  • stabilized output, low ripple & interference
  • short-circuit & overload protection
  • high efficiency & low energy consumption









This switch mode regulated power supply wall adapter comes with 4 input plugs to operate around the world. Includes input power plugs for the US, UK, Europe, Taiwan, and China! Additionally, choose from 7 different DC output connectors. Finally, a switching power supply adapter with a user selectable output plug size and polarity!

Get rid of those bulky power-hungry heat-producing linear power adapters. These switching power adaptors are state-of-the-art switch mode power supplies featuring major advantages such as:
– cooler running
– stabilized (regulated) output
– short-circuit and overload protection
– compact design
– very low idling power consumption
– multiple (selectable) voltage outputs
– user configurable output connector polarity: center (+)  or  center (-)
– world wide AC input voltage range


  • 4 AC input power plug configurations included (user selectable)
    • AC plugs to fit in US, UK, Europe, Taiwan and China
  • compact switch mode regulated power supply design is light-weight and efficient


  • AC input supply voltage: 100 ~ 240V AC, 50/60 Hz
  • output power: 24.0 watts max.
  • efficiency: > = 70%
  • user selectable output voltages:
    • 3V,  4.5V,  6V, 7.5V, 9V, and 12V DC
  • output current: 2,000ma (2 amps) maximum current consumption
  • 7 DC output connector plugs included (user selectable)
    • 2.5mm (male)
    • 3.5mm (male)
    • 2.35×0.75mm (female)
    • 3.5×1.35mm (female)
    • 4.0×1.7mm (female)
    • 5.0×2.1mm (female)
    • 5.5×2.5mm (female)
  • power supply dimensions: 4.6″ x 2.4″ x 3.3″  (11.6cm x 6.1cm x 8.3cm)







Brand Velleman
Supply Voltage 100 ~ 230V AC ± 15%
Power 10W
Efficiency > 80%
Output Voltages 3, 4.5, 6, 7.5, 9, 12V DC
Output Current 800mA (regulated) / 1.5A max.
Plugs 2.5mm mono, 3.5mm mono, 1.0×3.0mm, 1.35×3.5mm, 1.7×4.0mm, 2.1×5.0mm, 2.5×5.5mm, 1.5×5.5mm
Dimensions 2.6″ x 1.1″ x 2.9″
Weight 3.0 oz
Features Get rid of those bulky power-hungry heat-producing mains adapters.
These adaptors use state-of-the-art switching power supplies and feature some major advantages such as:
– cooler running
– stabilized output
– short-circuit and overload protection
– compact design
– very low idling consumption

Power supply units(PSU) are an essential component of any computer: in essence, PSUs provide all the power necessary to your computer by converting AC to low-voltage DC power. Sadly, however, many people do not realize its vast importance to the performance and durability of a computer.

StarTech AT Replacement Power Supply

Combining a shoddy PSU with an expensive computer can cause a variety of problems, such as a power surge damaging expensive computer parts, or crashes and reboots caused by the power level’s failure to support the system. Therefore, selecting the right PSU is essential to having a great personally built computer.

In general, when you are selecting which power supply is best for your needs, there are three main things to think about: 1) a power supply that fits your computer, 2) supplies the correct amount of power, and 3) possesses the correct connectors for your computer’s components.

A Size and Shape that Fits

Power supplies come in a variety of different sizes and shapes called “form factors.” The form factors of the computer case and power supply should match up. If they don’t, the power supply won’t fit.

In general, there are two main types of form factors for computer cases: the ATX (Advanced Technology Extended) and BTX (Balanced Technology Extended). The mid-size ATX is the most common size of computer case and will fit most power supplies. But be careful, because there is a full ATX which houses a much larger motherboard, and will be enormous compared to a mid-ATX sized power supply.

An Appropriate Amount of Power

The next step in determining the correct power supply is to figure out the appropriate amount of power your computer needs. According to, power supplies have two different wattages to pay attention to: true wattage and max wattage. “Max wattage shows the maximum power that particular unit can supply and it is almost never reached during every day use. True wattage shows the actual wattage which the PSU will supply most of the time.”

The Information for Voltage and Current Levels

Thus, it is more important to know the true wattage of the computer over the max wattage.

Furthermore, the amount of power a computer needs is based on the internal components and how much power they use. Computers will use and need more power if they house high-end graphics cards, powerful processors/motherboards, and multiple disk drives.

As a rule of thumb, its always better to buy a power supply with 50W-100W over the recommended power needed, so you can always expand your computer’s capabilities later. You never want to buy a power supply and then later realize it won’t suit the future additions you might add on. This PSU calculator is a good guide to determine how much power you’ll need.

The Correct Connectors

Another important factor in selecting a suitable power supply is to choose a power supply with the proper number and types of connectors. There are different molex and SATA connectors. Motherboards, processors, and PCI expansion cords all come with various types of connectors, so be sure all those parts line up with the power supply you choose. You can go the route of obtaining adapters, but remember not to have too many cords or adapters in your computer, which can impede the air flow within the computer tower and thus overheat your power supply.

The Variety of Power Supply Connectors

Other Things to Think About

Finally, there are a few other important things to think about when selecting the right power supply. I’ll only briefly mention these here:

  • Energy efficiency
  • Cooling fan – type, as well as how much noise it makes
  • Brand name CPUs vs. generic power supplies

Here are some of Eio‘s more popular computer power supplies:

Athena Power AP-MFATX25P8 20+4Pin 250W Single 80 PLUS Certified Server Power Supply

APEVIA ATX-JV650W 650W ATX12V/EPS12V SLI Ready CrossFire Ready Power Supply

See also: