How important is the power transformer in the whole equipment?
Like the reservoir energy storage power generation, the switching transformer can output electricity through the secondary winding at the same time, or can it output electricity through the secondary winding only after the charging is completed, just like the charging and discharging of the rechargeable battery? the answer is: both, as long as the core of the switching transformer is not supersaturated.
For the transformer energy exchange process in which the primary winding is charged and the power is output through the secondary winding, it is called "forward excitation" (analogy to reservoir energy storage power generation). For the transformer energy exchange process which outputs electricity through the secondary winding after the primary winding has been charged, it is called "flyback" (analogy is that the rechargeable battery is charged and then discharged).
It can be seen that "forward excitation" and "flyback" are actually not the distinguishing criteria made according to the transfer direction of energy (the direction of any switching power supply is fixed, from the primary winding to the secondary winding), but according to the time of energy transfer. Therefore, forward excitation and flyback are essentially a time concept related to energy storage, transmission (release).
For the "single-tube forward" and "double-tube forward" ATX power supply, the main switching transformer has begun to output power to the subsequent rectifier circuit through the secondary winding while the primary winding is charged. This is the meaning of "positive" in "single-tube forward" and "double-tube positive".