To calculate the power supply capacity for a specific device, its components must be identified, particularly those with more energy requirements. In computers, these are usually the motherboard, the graphics card, the hard drive, etc.
Each of these components will have an energy requirement expressed in watts. The sum of these values will be the required capacity. However, to ensure the power supply’s proper operation, it is necessary to calculate a margin of safety that’s between 10% and 20%.