Determining whether your cord provides AC (Alternating Current) or DC (Direct Current) power is usually straightforward by checking the labels or, for a definitive measurement, using specialized equipment.
Most cords that connect devices to wall outlets are designed for either AC or DC power. The power supply unit, often a brick or lump on the cord itself, converts the wall's AC power to the DC power required by many electronics.
Checking the Label: The Easiest Way
The quickest and most common way to identify the power type is by looking at the labels on the power supply unit (the "brick"), the cord, or the device it powers. Manufacturers include symbols and text to indicate the input and output specifications.
- Look for Symbols: Standard electrical symbols clearly differentiate between AC and DC.
- AC (Alternating Current): Represented by a wavy line or tilde (~).
- DC (Direct Current): Represented by a solid line above a dashed line (⌂).
- Read the Text: The label will often explicitly state "INPUT: AC" and "OUTPUT: DC" (or AC) followed by voltage and current ratings (e.g., "INPUT: 100-240V ~ 50/60Hz" and "OUTPUT: 12V ⌂ 2A").
Examples of Power Supply Labels:
| Label Section | AC Symbol/Indicator | DC Symbol/Indicator |
|---|---|---|
| Input | ~ or "AC" | |
| Output | ~ or "AC" | ⌂ or "DC" |
If the power brick's output section shows the DC symbol (⌂) or "DC", the cord coming from that brick delivers DC power. If the output shows the AC symbol (~) or "AC", it delivers AC power. The cord plugging into the wall is almost always receiving AC power from the wall outlet.
Using an Oscilloscope: A Definitive Test
For a precise technical determination of the power type flowing through a cord's output wires, especially from a power supply, you can use an oscilloscope.
According to technical references, you may use an oscilloscope to determine whether a signal is AC or DC. If the output when the output wires are connected to the oscilloscope has a sinusoidal waveform, it is AC. An output of direct current (DC) is represented as a straight line.
- AC Waveform: An oscilloscope displays AC voltage fluctuating over time, creating a characteristic wavy pattern, typically a sine wave.
- DC Waveform: An oscilloscope displays DC voltage as a steady, straight horizontal line because the voltage remains constant over time.
Using an oscilloscope provides a visual confirmation of the current's behavior, leaving no doubt about whether it is alternating or direct.
While checking the label is sufficient for everyday purposes, an oscilloscope offers a way to analyze the electrical signal itself for verification or technical troubleshooting.
