Lionel,
Paralleling switchmode converters for higher current is not straight forward. as with any voltage regulated source, the highest voltage will supply all or most of the load current while the other just idles. It is possible though with carefull adjustment of output voltage & placing a low resistance power resistor in the +out lead of each supply to achieve improved current share capability.
But there are tradoffs such as response time (ability of converter(s) to react to changes in load current) , wasted energy in the resistors.
You won't get double the current but maybe 175% depending upon resistors used & how accurate the converters current share.
This is could work but depends what the load is.
Also the 2 converters may drift in output voltage(eg with temperature/age).
Selecting the resistors is a tradeoff between current share balance, power dissipation in the resistors & tolerable response time.
There are some IC's to implement current sharing between converter outputs, more complex than the resistor aproach & again there are tradoffs, but if the load is not critical then should not be a problem.
If you were to place 0.1 ohm resistors on each converter +output, & assuming 7A current from each converter then the resistor will drop 0.7V & waste 4.9W each. This is not a recommended value of resistance but give you a starting point. it could depend how accurate the converters can be adjusted (most switchmode converters have output trim adjustment.).
I would use 2 x 50W aluminium housed(eg: Arcol) resistors mounted on metal plate.
Measure the voltage across each resistor to guage the current sharing of the 2 converters.
Also keep the wiring balanced as well.
Note also if your switchmode converter has a spec of 8A & you wish to draw 8A from it. This spec might be at 25 degC. & at its rated voltage (eg: if you trim up to compensate for volt drop across resistors the total power output might be exceeded.
eg 8x24V =92W, 8x25.4V = 203.2W
Pulling full rated power from a power supply all the time will likely reduce its life considerably but this can depend on the specific unit & how well it has been designed.
In our industry power supplies are used up to 30% to 50% of rated capacity to maintain reliability mainly.
Resistors we use up to 40% of rated wattage. eg For 4W power we use a 10W minimum resistor.
Toni G .au