ATX power supply minimum load
Over 20yrs ago a PC PSU would not perform as well as today and required some preload up to 10 % when good performance was expected with no load.  

Today I have not had this experience and can easily operate all outputs with no load.  So,there is no minimum load spec.  The Intel spec is for no damage to the unit but shutdown is permitted.

Since the most common design uses a multiwinding shared transformer to define the output voltage ratios , feedback on only needed on the primary output. That used to be 5V out for current but now is 12V with options for a secondary 12V with independent regulation for less load crosstalk between peripherals and GPU.

Your performance may vary and every design may be different. I might test it then add 5% preload if it shuts down after a transient load on your project,