Regulated vs Unregulated Power Supplies
Have you ever measured a "12V" power adapter with a digital multimeter and saw 16V, 17V, or 18V? You are testing an unregulated power supply. Understand why this happens and why connecting it to modern electronics can cause damage.
Constant Fixed Voltage
Features active feedback circuitry (SMPS or linear regulator) that maintains exact specified voltage whether drawing 0mA (idle) or 100% full rated load.
- • No-load voltage: Exact (e.g. 12.0V)
- • Full-load voltage: Exact (e.g. 11.9V – 12.0V)
- • Safety: Safe for all microcontrollers, hard drives, and modern electronics
Load-Dependent Voltage
Contains only a transformer, diode rectifier, and capacitor with no voltage regulation IC. Voltage spikes significantly above rated level when load current is low.
- • No-load voltage: 15V – 18V (+25% to +50% overvoltage)
- • Full-load voltage: 12.0V (only reaches 12V at 100% max current)
- • Hazard: Low-current devices connected to it receive continuous overvoltage
How to Test Your Power Adapter with a Digital Multimeter
- Set your digital multimeter to DC Voltage (V⎓) mode on the 20V range.
- Insert the red positive probe into the hollow center opening of the DC barrel plug.
- Touch the black negative probe to the outer metal cylindrical barrel shell.
- Interpret the reading:
- • If a 12V adapter reads between 11.8V – 12.2V: It is Regulated and safe for modern devices.
- • If a 12V adapter reads 14.5V – 18.0V: It is Unregulated. Do not use on sensitive electronics.
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