As an example certainly say 3 5vdc power supplies can have their outputs wired in series to make available +5, +10, and +15 volts relative to negative terminal of the 'bottom' supply, as long as the supplies have isolated outputs relative to their AC input terminals.
Your use of 'ground' term is taking on a more important role then it is in reality. In the above series supply example one could use the positive terminal of the 'bottom' supply be called and used as 'ground' and therefore have available -5vdc, +5vdc, and +10vdc. What you use and call 'ground' should rather be called 'circuit common' or just 'common' to make it clear that you, the circuit designer, is the one that determines what circuit point is to be common and all other voltages are relative to that circuit common point.
Ground, earth, circuit common terms can be confusing to newcomers (and some old-timers) and usually requires more 'system context' to best describe what is trying to be confided in the circuit schematic.