Why does PWR-01 series not deliver its rated current at its rated voltage?

The rated output voltage and current are limited by the rated output power.
For example, PWR401L has a rated output power of up to 400 W, so setting the maximum output voltage to 40 V and the maximum output current to 40 A would exceed the 400 W limit.
Please configure it with an output setting, such as 10 V and 40 A, that is within the 400 W limit.
For the details, read the user’s manual – chapter of Specifications – Output.