The reason we don't recommend to use a switching power supply for the motor driver is because the SmartDriveDuo-30 is a regenerative motor driver.
It means that when the motor is slowing down, the motor will generate a back EMF voltage and this energy will flow back into the power supply.
If a battery is used, the regenerative energy from the motor will charge the battery. However, if a switching power supply is used, the current cannot flow back into the power supply and this will cause the voltage to rise. If this voltage spike is higher than the absolute maximum voltage that the motor driver can handle, it will be damaged.
Other than that, it might cause your power supply to trip due to overvoltage too.
Since you have access to oscilloscope, you can probe the voltage while the motor is slowing down. If this voltage spike is within the limit, then you will be fine. How much the voltage spike is depending on the load and the deceleration of the motor.
Besides using a battery, you can consider to connect a shunt regulator (https://www.cytron.io/c-shunt-regulator ) in parallel to your power supply to absorb the current. Make sure you choose the right voltage level for the shunt regulator.