assuming they are switch mode power supplies

when connected in parallel to get more current than any one can supply
the odds are only one power supply will supply most of the current

usually its the very expensive power supplies designed to be connected in parallel that will share the load


when connecting them in series to get 48V you could be lucky but,
it is likely that one will fail to start and be reverse biased by the working supply
this will damage the electrolytic capacitors on the output side of the non working supply

John