Need help to find correct values for dummy load resistor
The dummy load would typically be on a supply that did not have the minimum current load applied. Typically you would place a load on either/both the +5 or +12 V supplies to ensure minimum load.
Since in most supplies they use co-regulation for +5/+12 or +5/+3.3 you may only need a load on one of them. Here is a typical PC power supply cross loading graph.  

 

Look at your power supply specs to find the minimum loads.
In the case above you could use a 25 Ohm load on 5 V, a 20 Ohm on 12 V and a 330 Ohm on the 3.3 V to meet all requirements.