The max output current rating of a power supply is a statement of how much current it can deliver consistent with its ability to regulate its output voltage, not overheat, etc.
The current drawn by any load connected to the supply is determined by the load; not by the supply. As a circuit designer, you simply need to determine if your load is within the capacity of the power supply. If your load requires only 1A at 12V, and you have a 12V 13A supply, that means that your load will only use about 7% of the supply's capacity. If your load requires 20A, but you have only 13A available, then you need to buy another supply.
Suppose you have a load which has a resistance of 10Ohms. You connect it to a 12V supply. How much current will it draw? I = E/R = 12/10 = 1.2A (Ohms law). Does it matter that the power supply capacity is 13A?
Now connect 13 such circuits to your 13A supply. Each load is 1.2A, so 13 of them would draw 13*1.2A = 15.6A, so your 13A supply is overloaded by 2.6A!!!
You need to measure how much each of your circuits draws at each of its voltage inputs. Use a Digital Multimeter temporarily connected in the positive lead to one of your circuits while it is operating. Add up how much total current you need at each of the voltages....