There are several ways to test a DC power supply, but here are a few common methods.

Continuity test: You can perform this test using a multimeter set to the continuity setting. Touch the positive and negative terminals of the power supply with the multimeter leads. The multimeter should beep if there is continuity. This test can help to determine if the power supply is providing power and if there are any broken connections in the wiring.

Voltage test: You can do this test using a multimeter set to the DC voltage setting. Touch the positive and negative terminals of the power supply with the multimeter leads. The multimeter should display the voltage that the power supply is providing. Compare this to the power supply's rated voltage to ensure it is within the correct range.

Load test: You can perform this test by connecting a load (such as a light bulb or motor) to the power supply and measuring the voltage and current with a multimeter. The voltage should remain stable and within the expected range, and the current should be within the power supply's rated current.

Ripple test: You can do this by measuring the AC component of the power supply's output voltage. You can connect an oscilloscope to the power supply's output terminals and measure the voltage ripple. The ripple voltage should be as low as possible and within the acceptable range.

It is important to test a power supply with caution by following the instruction manual and safety guidelines. Also, if you are unfamiliar with electronic testing, consulting a professional or using pre-built testing equipment is better.