Power Supply Symbols

The rating plate of an Extra Low Voltage Power Supply Unit (ELVPSU) shows various symbols and abbreviations representing ratings, class, insulation, polarity and other electrical safety and EMC compliance details.

DC Adaptor Polarity Symbols

The polarity symbol on the rating plate of an AC to DC power supply indicates if the centre (or tip) of the output plug is positive (+) or negative (-). It is important to use a power supply having the correct polarity for the host device. Reverse polarity may result in malfunctioning or damaged equipment.


Centre Positive.

Indicates that the centre (tip) of the output plug is Positive (+) and the barrel of the output plug is Negative (-).


Centre Negative.

Indicates that the centre (tip) of the output plug is Negative (-) and the barrel of the output plug is Positive (+).


The following abbreviations used in conjunction with a numeric value, are used to define nominated electrical characteristics of a power supply unit.

V volts Hz hertz
A amperes PRI input
mA miliamperes SEC output
VA volt amperes DC direct current
VAC volts AC AC alternating current
W watts ~ single phase (AC)

Other Symbols

These symbols are used to define the type of construction and safety and/or fail-safe characteristics of a power supply unit

Direct Current Image
Direct Current

Protected Earth

Class II construction

Isolating transformer

Safety isolating transformer

Fail safe transformer

Fuse link

Frame or core terminal

Non-short circuit transformer

Short circuit proof transformer

Fail safe transformer


C Tick Symbol

A C-Tick mark appears on products which are required to comply with Australian electromagnetic compatibility requirements and with Australian radiocommunications standards.  It signifies that the product may be legally sold in Australia. 

Regulatory Compliance Symbol

Regulatory Compliance Mark

The may be used as an alternative marking to show compliance with Electrical Safety and EMC standards