DC Power Limiting Circuit
PSUs aren't designed to operate in parallel and "share the load". 

This is because each PSU will have their own feedback loop to set the output voltage. The output voltage is set from an internal reference. These references can never be exactly the same so the PSU's output voltages will always have a (small) difference.

The PSU with the highest output voltage will "win" and it will set the voltage. Then the other PSU will simply stop outputting any power since its feedback loop determines that the output voltage is higher than what it thinks it should be. So that PSU with the lower output voltage will simply not deliver any current.

Only when you (over) load the PSU with the higher voltage so much that its output voltage will drop can the other PSU "kick in" and deliver current. But then the load isn't balanced at all, the PSU with the higher output voltage is (over) loaded / loaded to its maximum and the low output voltage PSU only takes a smaller part of the load.

This cannot be fixed without opening and modifying the PSUs (which is NOT RECOMMENDED) and even then some complex circuitry might be needed. That's why no one does this.

There is a much, much simpler solution: just buy a PSU with a power rating such that it can power the load on its own.