Fuse PK Insurance Resistance Really insured?

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According to the traditional theory of electronics, a fuse, in particular a switching power supply, must be connected in series to the front of the power supply. When an abnormal situation arises such as a short circuit in the power supply, the fuse will blow and cut itself off to prevent further expansion of the fault.
In the process of contact with the power supply, I found a problem that the power supply was damaged during operation. The internal circuit of the power supply was short-circuited and resulted in high current. According to the conventional understanding, only the fuse should be quickly blown and there would be no other impact. However, in our communication with our guests, we found that this is not the case. There will be a certain chance of air switch tripping, copper burst on the power board traces, and smoking. When it is bad, the movement will be quite large and it will be shocking. Since the fuse burned, it is said that these conditions will not occur, it seems that the reasons are worth analyzing.
Let's start with a schematic diagram to explain where the copper skin burst and let everyone understand the problem representation before we can understand and analyze it...

When the power supply is damaged, if a short circuit similar to the one shown in Figure 1 occurs inside, the fuse will be burned. In actual applications, we find that sometimes the position of the “burst” character is too large and the copper skin is burned and burned. There are even occasions when bridge foot's feet are blown.
It seems that although the fuse is also blown, but it did not play the desired effect. When the fuse was blown, the internal short circuit of the power supply further caused the damage of some circuits. The response speed of the fuse seems to be a bit slow, and there is no expectation. So fast.