PSU Upgrade

The fact that the components will only draw what they need and not be force fed by the psu.

The same reason when you plug in your phone it does not fry it.

Power supplies supply a fixed voltage, they have current available to be drawn if needed but they do not push the current down the lines, they maintain the voltage and as the part needs more power, its resistance drops and more current flows into to feed it, but only as much as it needs.