How to get higher amperage out of a power supply?
If the power supply outputs can be put in series (i.e. their 0V ends can be "lifted" from ground) then you get 48V @5A and you can probably get a cheap off-the-shelf buck regulator that will convert down to 24V @9A. If you were designing from scratch I'd consider this part: -



The above circuit is shown generating a 12V output from inputs ranging from 15V to 60V. If both power supplies are connectable to produce one at 48V then the above circuit, with ratio modification to the two resistors in the red box will easily produce 24V. However, I'm sure you could pick something up from a chines source or ebay for ~$10.

If they both have to be grounded then you could use a H-bridge driver chip where one half of the H bridge is powered from one supply whilst the other half is powered from the other 24 v supply. Maybe something like this.

Or you could have both supplies individually driving their own 12V flyback converters and wire the outputs in series (transformer outputs are used in flyback converters). This will work too.