Have you ever been in a situation where you needed to test a device with both a negative and positive voltage? Many people come across this situation and think they need some kind of special tool to do this. When in fact, they only need two single power supply units or one triple power supply unit.
For example, the Korad KA3300 Series triple power supply units have this capability. In order to create the negative charge, the leads must be plugged in according to the picture below.
If you take a close look at the bottom right hand corner of the unit you can see that this KA3305P is in series mode. It is possible to do this by reversing the leads on a single power supply unit. But it can damage the transformer after prolong use. Also, notice how the leads need to be placed in the negative terminals this is because of the series function. This is the connection setup for a negative voltage in series mode.
For a positive voltage, look at the following picture for the proper connections in series mode:
Triple power supply units allow a user to use two voltages simultaneously without the worry of needing to switch leads.