How is the power consumption calculated if a step-down power supply is used?

Question

Electronics

Please explain on your fingers) why the power consumption of the power supply is calculated based on its low side of 9 Volts 0.6 Amperes, and not on the high side of 230V 0.3A ???

Answer 1

Because this is NOT the power consumption, but the rated output power of the power supply.

Answer 2

You are confusing input and output power. By the output current and voltage, you can determine how much the PSU gave to the load, and by the input - how much it consumed from the mains (that's what you need). The ratio of the first power to the second is called efficiency, usually expressed as a percentage, and naturally, it can never exceed 100% (although everyone really wants this).
Further, your 0.3 A is most likely marked on the case as "no more than 0.3" - i.e. this is the maximum allowed value. This figure cannot be used to determine power. The real current to determine the power consumption must be determined using an ammeter, when connected to a PSU of a specific load. If it is not connected, then a small current consumption will still be - it is due to the PSU's own consumption, thereby, due to which the efficiency can never reach 100%.

Answer 3

power is written true. if the power supply can drive only 9 * 0.6 = 5.4 W through itself, then it is written like that or roughened down.
for the "high" part, they usually write
the supply voltage 230V
, the current consumption is not more than 0.3A.
usually it says that there is a 0.3 A fuse at the input and the unit, even with a short circuit in the circuit, will not consume more than 0.3 A.
this is not about power, it's about safety.