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Power Supplies A to Z : "U"

We've included this handy glossary to help with the terminology & abbreviations relating to power products. Pick a letter below to begin, or download the glossary to refer to it whenever you like.

A B C D E F G H I J K L M N O P Q R S T U V W X-Z #


Unit of height (usually) in a 19 inch rack. 1 U = 1.75 inch = 44.45mm.


Abbreviation for Underwriters Laboratories Incorporated.

Under voltage Protection

A circuit that inhibits the power supply (PSU) when the output voltage falls below a specified minimum.


A transient change in output voltage outside of specified regulation limits. See Overshoot for a drawing to illustrate undershoot.

Underwriters Laboratories Incorporated (UL)

USA based safety agency. See

Uninterruptible Power Supply (UPS)

A type of power supply (PSU) designed to support the load for specified periods when the line varies outside specified limits. Generally they are powered by ac (with battery operation taking over when the ac supply fails) and supply ac on their output. Most likely to be used to protect telecommunications equipment and computer systems.

Universal Serial Bus (USB)

A serial Communications Bus now standard on all new PC's. Suitable for communication between one controller (computer) and one or more pieces of equipment (power supply, etc.) See Communications Port.


Abbreviation for Uninterruptible Power Supply.


Abbreviation for Universal Serial Bus.

A B C D E F G H I J K L M N O P Q R S T U V W X-Z #

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