This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC’s registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726. At the system level, there are ac and dc power analyzers. At the subsystem level, a considerable amount of test and measurement systems can ensure a power supply is working properly. Testing at the component level mostly involves the power semiconductors employed in the system. RMS (Root mean squared value) is the most commonly used and useful means of specifying the value of both ac voltage and current. The RMS value of an ac waveform indicates the level of power that is available from that waveform, which is one of the most important attributes of any ac source. Because the output current of a switch-mode power supply is not sinusoidal, the crest factor of the current waveform can be much greater than  √2 Real Power is the power available to the load to do real work and is given in Watts. With a pure resistive load, you can multiply the RMS voltage and RMS current to get real power. Reactive Power is the vector difference between Apparent Power an...