Are you connecting the two outputs in series (24 V at 8 A) or parallel (12 V at 16 A). Each way might have issues depending on how well the power supplies are designed.
With the series connection, the output noise will be greater. Also, at startup one of the supply outputs will come up before the other, and appear aw a reverse-connected power source driving the output stage of the later supply through the system load. That reverse connection might be seen as a fault and prevent the 2nd supply from starting up. To prevent this, put a power diode across each supply output reverse connected. This will prevent the reverse connection from exceeding 1 V, usually low enough that the 2nd supply does not see a fault.
With the parallel connection you can do what is called diode OR-ing or droop sharing. Connect the two +12V outputs together through power diodes. The diode's forward voltage drop acts as a ballast impedance. If you carefully adjust the two supply output to be the same voltage, you can get good (but not excellent) current sharing between the two supplies into the load. When we do this, we assume the sharing will never be better than 75%, and that is with the two diodes in one package so they are thermally connected. Output voltage regulation suffers, but you can combine almost any two supplies.
ak