P4400 power meterPC power supplies generally last several years so they qualify as durable goods. The EPA however recognized that a lot of power was being wasted with obsolete designs so they embarked on their Energy Star campaign. For background, see the page on the ATX power supply.


We use a low cost PSU tester that shows green for each voltage. It has connectors for all of the standard PSU connectors including EPS12V and SATA. It can even help identify damaged cables. More recently a new model with a LCD display now shows the voltages.

Thermaltake Dr. Power II Automated Power Supply Tester Oversized LCD for All Power Supplies


We use a digital clamp meter which has the capacity to handle up to 600A of current. We also have a x10 loop which can be used to monitor small AC 120V power loads. The clamp meter has the conventional connectors for banana plugs so that it can be used for general electrical work.

If the yellow wires are separated away from the black ones, the clamp ammeter can measure the current. Modular cables can be easily separated apart for careful load testing,

Fluke 323 True-RMS Clamp Meter


Low cost testers like the Kill a Watt P4400 can monitor the power consumption of any appliance. The P4400 can be a real eye opener as it can calculate the kWh of power used by an appliance. It’s designed to be installed between the appliance and the plug in the wall.

The P4400 can measure power loads almost as good as the digital clamp meter, Some charts on some review sites show the load of a machine with each of several cards installed. In the real world loads are not static so the P4400 is better off being used long term.

The P4400 really is designed for longer term use. It can show the actual power used over time. It can also show how a new 80 PLUS good PC power supply can save a bundle in electrical costs over time.

P3 International P4460 Kill A Watt EZ Electricity Usage Monitor


This requires measuring the input power and the output power at the same time. The ratio is the efficiency. 80 PLUS bronze requires 82% efficiency. 80 PLUS gold requires 87% efficiency. The P4400 monitors input power easily in addition to calculating kWh usage,

Static load testing is not very realistic with gaming. This means that at times the machine is at idle or sleeping. Power supplies can be less efficient at standby and work has been done to try to remedy this problem..

Recent 80 PLUS platinum power supplies re now reaching 94% efficiency.As prices fall these will go far towards improving the overall efficiency of everyone’s machine. .


Some reviews like to load test a power supply, Today most power supplies can deliver their stated capacity. Counterfeit power supplies are still a serious problem. A more reliable measure is the P4400 and the actual kWh consumed over time. Its best to use the P4400 continually and with a journal it can be a powerful tool.

It’s not a good idea to cut corners with power supplies.A good rule of thumb is to have 50-100% extra capacity. Power supplies are at peak efficiency with a 50% load.

The simplest dummy load is using power resistors. 12V and 100A needs 0.12Ω. Resistors in parallel increase power and lower resistance. 50W resistors are mass produced. They are easily attached to a heat sink which allows the load to be used continually. High power assemblies need active cooling.

Using simple pins it’s possible to connect all the 12V cables to be sure the overall capacity can be stress tested. Using separated yellow and black cables allows the use of the clamp meter for extreme loads.

We use a low cost 200V 100A panel mounted digital ammeter. A 200A shunt is more than adequate as the top Corsair PSU only reaches 120A maximum. THis makes it easy to monitor loads.


Digital volt meters all use operational amplifiers for comparators. Bipolar operational amplifiers are very versatile. Microprocessors use a MOSFET version of an operational amplifier.


Remote USB thermometers are capable of storing temperatures over time. The are able to run for more than a month without power. Taping one to the exhaust fan of a PC power supply will easily show that temperatures can be > 10°C above ambient. Modern 80 PLUS gold and better rated power supplies have sharply lower exhaust temperatures. The low cost Corsair CS450M, for example, quickly pays for itself when retrofitted into refurbished machines.


Fans make noise. The load tester makes a lot of noise thanks to a bank of needed fans. This makes it impractical to test noise in any meaningful way. Modern 80 PLUS gold and platinum power supplies have started to offer zero fan when the heat is below a threshold. Better motherboards have more fan control which can reduce noise, Video cards with 2 or 3 fans run much cooler. They also make a lot less noise.