Firstly check your power supply is outputting 12V to the console.

After that, press the power button to see if the system gets a beep at least (it may only beep and not power up or go any further, but if you at least get a beep continue on).

With mains power applied, and the in-build power brick sending 12V to the console, you can check some main regulators are outputting expected voltages.

The 12V from the power supply should make its way to all the row of large capacitors near the bottom of the console.

Located usually the bottom left of USB ports.

Confirm if the regulator has 5V input, and the inductor has 3.3V output.

Located under the FFC ribbon that connects to the DVD drive, near the fan side.

Confirm if the regulator has 5V input, and the inductor has 2V output.

A quick place to check the standby 1.8V is present is a capacitor near the USB ports.

At the same time as checking that, you can press the power button on the PS5 to make it beep, and you should get the 1.1V rail appear.

All around the console are various fuses to check. They are labelled F7001, F7002, F7003, F5401, F5402, F3501, F7501.