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 (+).
Abbreviations
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 |
 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
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 Mark
The may be used as an alternative marking to show compliance with Electrical Safety and EMC standards