Depending on the requirements, laboratory power supplies are available in a wide variety of designs with one or more fixed or adjustable voltage limits, fixed or adjustable current limits and for different power ratings. Tracking-capable laboratory power supplies can output symmetrical output voltages with different signs but the same magnitude. Laboratory power supplies always have regulation, at least for the output voltage, often also for the output current. They can be designed with a mains transformer, rectifier and linear control or as a switched-mode power supply.