Any power supply output needs a reference to ground. It can not be floating.
If it were floating and its cables pass next to other cables with strong dv/dt like those that use PWM, voltages in the range of thousands volts can be induced respect to earth in the floating side.
For avoid this the usually way is to connect the 0V output to ground but only at one point, usually at power supply output terminal, but never use the ground circuit as power supply common. The common must be a separate wire.
Of course to achieve this the power supply must have the output isolated from input. The same applies for transformers.