Depending on 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 capacities. Tracking laboratory power supplies can output symmetrical output voltages with different polarity but the same amplitude. Laboratory power supplies always have a 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 switching power supply.