Advances in power electronics have lead to a shift from relatively large and heavy transformer power supplies to smaller, lighter and more efficient switching power supplies. They can be found today in almost all electrical devices that are connected to the 230V mains. While they avoid many disadvantages of their predecessors, they also bring new challenges: First, the system perturbations are not negligible by harmonic and must be limited by standards (EN 61000-3-2, EN61000-3-12). Secondly, the high switching frequencies of up to several hundred kilohertz, on both, the network side and on the consumer side, lead to problems with electromagnetic compatibility. Task of power measurement technology is to help manufacturers optimize their products.