How To Test a Power Supply

Last updated: November 25, 2022 at 11:10 am

Every professional technician understands that a stable, well-regulated power supply is required to perform consistent and reliable circuit and subsystem tests. However, what about testing a new power supply, converter, or regulator design? 

It’s not challenging to determine a faulty power supply as the main reason for an equipment failure. However, not all problematic power supplies have the same malfunction source. Frequently, overheating causes failure. Other times, it is a capacitor failure, and semiconductor failures are more frequent. 

Getting to the bottom of your power supply failure indicates properly assessing the component malfunction/s that caused it. A professional technician will depend on a good power supply tester or a multimeter. It’s a device that can run diagnostic tests to troubleshoot electrical parts. 

This post will explain more about that in detail. 

What Is a Power Supply and Why Do You Need to Test It?

Please don’t confuse a power supply with a power source. Remember that the source is the origin of incoming electricity. Often, the electricity source is a generator, battery, or outlet. The power supply converts the power from the source into the proper voltage and format.

Since a selection of options exists, the particular power supply function varies depending on whether it should convert or regulate energy. To better know what a power supply is and how it works, you should learn its components and their contribution to the device’s operation. 

Power supplies have integral functions in every model, with extra operations included based on the device type. Power supplies may need to modify the voltage up or down, regulate power for smoother outcoming voltage, or convert power to direct current. 

Also, getting a device with many features could cost you more expenses than you must spend. However, you need to get the features to avoid easily damaging the devices you need to power. 

After repairing and troubleshooting a power supply, load testing is essential. Repair technicians will use a multimeter and other tools to test the power supply against field conditions to gauge a series of vital variables. 

Guarantee repeatability 

Testing for repeatability guarantees the power supply does not immediately succumb to the same problem that brought it in for repairs, like a faulty diode. Also, repeatability indicates a unit is prepared to do as expected consistently. 

Confirm compliance against regulations 

Repaired power supply units should meet manufacturer and equipment supply load and power factor recommendations. Checking compliance against regulations indicates meeting OEM standards for functionality and safety, so there is no risk of liability if potential problems happen. 

Calibrate against a standard 

Load testing to a standard guarantees the supply is offering power at a rate consistent with the reading. For instance, testing against ten volts guarantees the power supply is putting out ten volts.

Calibrating against the standard also indicates sending the power supply back into the field along with the same performance expectations as the factory specified. 

Check performance 

Ensuring the repaired power supply working is only part of quality control. Maintenance personnel must perform a detailed check irrespective of any other concerns. 

A quick load test will determine whether the power supply is free of the original problems and can offer a constant current. 

Each of the above variables plays a crucial role in ensuring the long-time function of a new fixed power supply. 

Common Test Tools for a Power Supply

A power supply tester is an electronic device that tests how well a device functions. You do this testing as part of maintenance on a computer to determine the source of an issue.

It’s a handheld device with various plugs that you can connect to the power supply within a computer. Here are some standard testing tools you can use for power supply tests. 

Wand voltage meter

It is a costly specialty tester owned only by professional and licensed technicians. This is a numerical voltage tester with electrostatic wands that could measure and detect voltage by holding them in proximity wires or metal contacts.

Digital clamp meter 

This tool combines the function of the current sensor with a multimeter. It’s a little bit more pricey than a multimeter. It is a specialty tool that homeowners will require unless they’re working with advanced electrical work. 

You’ll find subtle differences in function between this and a multimeter. The most obvious one is that it boasts clamping jaws, which could grip wire conductors. That makes the tool easier and safer to use in other applications. 

Solenoid voltage tester 

Professionals often utilize this over a multimeter because of its ruggedness and don’t have batteries to monitor. Nonetheless, it is not as accurate as a multimeter for offering numerical measurements of how much voltage there is. Still, it’s less pricy than a multimeter. 

Both digital and analog models are accessible. These power supply testers have two wires, each with a probe spreading out of the tester’s probe. They announce the presence of voltage by vibrating or clicking. The more pronounced or louder the clicking is, the higher its voltage level. 


These are flexible electrical testers that can test numerous functions. Many multimeters can offer exact resistance, frequency, capacitance, continuity, and AC and DC voltage readings. Therefore, they can offer all the data other electrical power supply testers provide. 

Remember that multimeters feature a boxy body with analog or digital readout, a dial for setting the test function, and two long leads with metal probes at each end. Such testers could vary widely in accuracy and quality, and you will need to pay more for quality. 

These tools are way costlier than the basic testers. 

Continuity testers

It is a reasonable battery-powered device with a probe at one end, a cord with another probe at the other, or an alligator clip. A light on the tester’s body indicates other units also produce sounds if there’s a total circuit.

Compared to basic voltage testers, you can use continuity testers when a circuit is turned off or on devices or wiring connected to the circuit. They do not test for the voltage’s presence but to determine whether an electrical path is intact in a device or appliance. 

Plug-in circuit analyzer 

These cheap, simple-to-use testers could tell you more about the circuit’s function when you insert them into an electrical outlet. Such devices test grounded outlets with three slots. You can’t use them on older 2-slot outlets. 

Also, plug-in circuit analyzers feature three neon lights lighting up in various patterns to tell particular test results. A chart sticker on the device helps you understand the light patterns. Various light combinations suggest a properly wired outlet, an open circuit, a reverse-wired outlet, and the presence or lack of a ground connection. 

You can find more advanced plug-in circuit analyzers telling you the voltage and its circuit conditions. That tool does need recharging or batteries. 

Neon voltage tester 

Also called neon circuit testers, neon voltage testers tell you whether the voltage is present. They do not tell you how much voltage is there in the circuit. They also have a tiny body with a neon light inside, two short wire leads, and a metal probe on every end.

That device also doesn’t use a battery, which makes it a reliable tool. It is cheap, as well. It is a simple-to-use tool, but you should handle it with care. Accidentally touching either of the metal problems can get you a shock.

Inductance tester 

This tool lets you check for voltage in devices or wires without touching any electrical components. They are simple to use, safe, and inexpensive. 

The device is like a small wand with a tiny tip on the end, sensing voltage in switches, light sockets, lamp cords, circuit breakers, outlets, or electrical wiring. You can receive a reading by sticking the tester’s tip into the outlet slot or touching the wire’s outside or the electrical cable. 

A power supply tool is a specialized equipment that most people will not buy. Other power supply testers, like multimeters, allow you to test a power supply. However, the entire process can be more challenging. 

You can use these devices for different applications, but they are more likely to be a practical investment for somebody who doesn’t perform computer repair professionally. 

How Do I Know If My Power Supply Is Faulty?

If you have any of these scenarios, you may have a failing or faulty power supply. 

You hear clicking or buzzing sounds from the computer. 

That’s probably one major faulty power supply sign. Coil whine is a nerve-wracking dilemma in which you often hear a high-toned noise caused by electricity passing through the transistor. The thing is that it occurs when the GPU is under load. 

You can check if it’s coming straight from the GPU or the case’s back side, where you can find the PSU. It is probably up for some replacements if you hear any grinding or loud noise from the PSU.

You observed a burning plastic smell or smoke from the PC case 

Have you ever observed a burnt smell on any smoke from the PC? You certainly have some damaged components. If you notice either of these two, power the PC down immediately, open the case and check the PSU and motherboard for physical burn damage. Often. It might not be apparent, particularly if it’s the capacitor.

You’ll hear a loud bang when overloading a capacity, suggesting it stopped an electric surge.

Your other PC components malfunction or fail 

The worst thing that could happen is hardware damage to other parts. That is why a functional PSU is important in sending the proper power to the parts. Do you notice a pattern of hardware failure, like the PC case fans continuously dying even when it’s brand new? There’s a high possibility that a faulty power supply damaged it. 

Your device can not properly start 

It is the most obvious sign that your power supply is faulty. You may observe that when you try to power the device on, no fans begin to spin, although there’s nothing wrong with them. If the PC does not have flickering lights during startup, the PSU fan does not spin, or there’s no picture on the screen, it is obvious that the PSU is dead. 

What Makes a Power Supply Go Bad?

Without a final quality check against your load, a power supply could experience a broad spectrum of concerns, leading to user hazards and machine downtime for businesses. They include the following:

  • Doing an incomplete replacement or repair
  • Using the wrong replacement part
  • Doing the wrong component repair
  • Instant supply failure the next time it is used due to repair personnel 
  • Transients sent to peripheral electrical components caused by a failure to control current through the power supply. 
  • Shock hazards due to existing overvoltage or an electrical supply which goes beyond compliance standards. On the other hand, brownouts caused by the sag in the supply convert into issues keeping the electronics running. 

Testing against the load guarantees correct performance before the power supply breaks. And it provides a final quality check that is essential in keeping the function and safety of vital power supplies instantly after repairs and long into the future. 

What Are the Common Power Supply Problems?

Here are some of the common power supply problems you need to know so you know when to act: 

Missing external parts

Power supply performance could be affected by missing external connections or components. The version uses a specific circuit, mimicking a standard application. If there’s no similar circuit applied during testing, the performance may differ from what we mentioned.

Another oft-missing set of components is pull-down and pull-up resistors. You need these to ensure a known voltage for off/on. For instance, a pull-up resistor makes an extra loop around vital components. It provides a well-defined voltage that stays even when the switch is open. 

Meanwhile, a pull-down resistor will hold the voltage close to zero when a switch is open. 

Temperature problems

Falling either over or under the suggested temperature range for a power supply is a common problem causing issues for a power supply. Thermal limits guarantee the power supply runs within the range where you could account for its performance. 

Efficiency, EMI, regulation, and reliability can become issues outside the maximum and minimum operating temperatures. Most parts inside your power supply, like transistors, run at temperatures close to their thermal limits.

Running the power supply beyond its rated temperature could cause such devices to fail. Moreover, other power supplies enable an extended temperature range, especially when a derated or decreased output power exists. 

Reversed polarity 

This issue involves improperly connecting a power supply’s negative and positive outputs or inputs. Most parts can’t tolerate reverse polarity and will fail when subjected to it. You have reversed the polarity on the power supply’s output connections.

You may notice a damaged load, possibly resulting in power supply failure. The worst thing it may cause is a destroyed circuit or electrical fire.

You can use a diode to safeguard against this problem in lower-power applications. You can place it in a series or anti-parallel with the output or input. When in series and if the voltage is reversed, the diode won’t conduct and keep the circuit open.

The only disadvantage of this tactic is that the diode will disperse power proportionate to the input current. The diode will normally be off and conduct when the polarity is reversed, especially if you put anti-parallel to the input. Also, the diode will short and activate an overcurrent protection device, like a fuse or the power supplies OCP, once it conducts. 

Input undervoltage and overvoltage 

Both overvoltage and Undervoltage can be problematic for power supplies, and they are one of the most typical problems people experience.

The source for these is improperly setting the 120/120 Volt switch on non-universal input. That switch disables or enables the voltage-doubler inside the power supply. Therefore, the internal circuits run at 240 volts in either scenario.

If you set it incorrectly, the internal voltage will either be too low or too high, leading to failure. Remember that power supplies with universal inputs run across the full input voltage range without using a switch and do not have this issue. 

Typical sources involve powering down and up machinery, touching the power supply by a charged object, and lightning strikes. Many power supplies will have some amount of protection from such cases. Depending on the application, you may need more or less immunity to such disturbances. 

Final Thoughts for Power Supply Test

When a hardware fault starts to cause havoc on your devices, it can be challenging to determine what’s causing all the problems. With a few symptom checks and tools, you can easily diagnose your issues and determine whether the power supply is at fault.

Also, remember that safety is your number one concern. A power supply test will guarantee it’s safe to use.

Are you trying to get the right power supply vendor? Let a reliable supplier provide you with high quality power supply solutions.

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