If you want to use a low power supply, you will become a high power supply yourself.

It is estimated that it is impossible to grow from small to large, regardless of the different principle of voltage stabilization, at least there are few small power components available at hand. In addition, it is complicated to spend money on components and printed circuit boards, which also violates the purpose of saving money.

Two power sources can be considered, but they cannot be connected in parallel and must not be electrically connected. They are only powered by two groups, and they are still independent power sources. One is the motherboard, hard disk and the like, and the other is the optical drive and the like, and they are equally shared.

One more question. Switching power supply will only supply power to the outside if it is triggered. The power supply plugged into the motherboard is fine, because pressing the motherboard power switch will trigger the power supply, while the group of power supplies that are not plugged into the motherboard will not get the trigger signal of the motherboard and will not supply power. You have to find the wiring plugged into this power motherboard, one of which is green (only one is different in color) and connected to the ground (any black line).