The situation you are talking about is a typical bad behavior of inferior switching power supply merchants who pass off substandard products.
The computer's switching power supply uses traditional bridge rectifier and capacitor filter circuits. This circuit structure will cause severe waveform distortion of the mains AC input current and inject a large amount of high-order harmonics into the power grid. And cause serious harmonic pollution and interference to the power grid and other electrical equipment. In 1982, the International Electrotechnical Commission formulated relevant specifications and began research on harmonic filtering and power factor correction (PFC) technology. PFC circuits are introduced into electronic power products. The full English name of PFC is "Power Factor Correction", which means "power factor correction". Power factor refers to the relationship between effective power and total power consumption (apparent power), also It is the ratio of effective power divided by total power consumption (apparent power). This can greatly improve the utilization efficiency of electrical energy.
There are two types of PFC, one is passive PFC (also called passive PFC), and the other is active PFC (also called active PFC). Passive PFC generally uses inductance compensation method to reduce the phase difference between the AC input fundamental current and voltage to improve the power factor.
The "metal block" you call is the inductor in the passive PFC circuit. Regular PFC inductors are wound with enameled copper wire on a high-quality closed iron core. All power supplies that achieve 3C certification must have a PFC circuit. Therefore, regular switching power supplies are equipped with PFC circuits. Some power supplies using passive PFC circuits are relatively heavier due to the addition of PFC inductors. In order to save costs, some low-quality power supplies use an iron block to pretend to be a charging inductor; others just use a plastic block with a sticker on the outside to pretend to be an iron core inductor. Such a power supply is unscrupulous in order to reduce the cost, and its poor quality can be imagined.
Therefore, when you encounter such a power supply, no matter what the name brand says, you cannot buy and use it. Otherwise, you will save a little money. At the least, it will cause frequent computer failures, and at worst, it will damage the board and hard disk. Causing your computer to suffer severe damage.