To connect in series, then in parallel is basically no problem if the outputs has series diodes. However if the units shall be programmable or use active current sharing, then care should be taken.
The Delta Elektronika labb power supplies has a parallel and series connection feature built in that can be used in manual mode. If such system shall be controlled by an external bus, then an insulation amplifier ISO-AMP shall be connected to each of the units with the system zero referense within the series connected units.
Polyamp PC1000 to PC2000 and PU1000 has an active current share signal. In such system the current share signal is only connected between the units connected to system zero. See below figure.