Mode A is more used in low-end entry-level power supplies, and this mode requires three pins from the transformer. Mode B is mostly used in high-end power supplies. This mode generally only needs to be equipped with two transformers, but the ferrite inductance must be large enough, so the cost of this mode is high, which is why low-end power supplies do not use this mode. main reason.
In addition, for high-end power supplies, in order to increase the maximum current output capability, these power supplies often use two diodes in parallel to double the maximum current output of the rectifier circuit.