Power supplies are made in many shapes and sizes, with most simply offering a fixed DC output that can be of varying quality and accuracy. There are many instances where specific levels and features are required and such circumstances usually involve the use of a laboratory power supply. Although they are useful in schools and laboratories, they have many other applications, including research, testing and quality control work. Highly accurate, fixed voltage power supplies are available, normally consisting of a step-down transformer and switching regulator, but for general purpose use, an adjustable supply offers greater flexibility. When an accurately controlled AC supply is required, the best choice is an adjustable isolating transformer. These are safety transformers with galvanic separation of input and output circuits. Voltage levels are normally displayed by a voltage panel meter. In many cases, the testing of equipment is made much easier by the use of a dummy load, or DC electronic load, which mimics the actual loads present in the completed final installation - such loads are available in varying degrees of complexity, many being suitable for use in high-volume manufacturing situations.