What are the applications for power supplies in connected in series?

There are two different applications when power supplies are connected in series. One is to generate plus minus voltage, another is to increase total output voltage. Connection methods are as follows:

(1) Connection for plus and minus voltage are shown as follow

(2) To increase the total output voltage (Output current remain the same). Diodes connect in parallel at output side of the driver is necessary to prevent damage during start up. The voltage rating of diode shall greater than V1 + V2(shown as figure below), in addition, peak forward surge current rating shall greater than rated current.

* Because part of the signal ground is shorted with output ground, strongly suggest to use isolated signals to achieve control scheme, in order to prevent damage to the product.