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Why is it many DC power supplies (for simpler systems that don't need amazingly clean power, for example) have a very low rates output power, e.g 12V 1A?

What makes a supply consisting of a 20:1 turn ratio transformer, full bridge rectifier and a capacitor not viable? Would that not, in theory, be able to deliver the full 2.4kW of a 240V wall socket (or thereabouts)

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    \$\begingroup\$ Sounds to me that you are describing a welder. Did you ever lift one? \$\endgroup\$
    – Transistor
    Commented Jul 12, 2017 at 14:57

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2.4kW at 12v would mean 200A.

There is no fundamental problem in principle with making a power supply like that. However, you've seen the size of cables used in your car to take 200A between battery and starter motor. The same would go for the diodes and transformer used in the supply. It would make for a very expensive piece of kit.

If you only need 1A to power your router, a 1A supply, with much smaller transformer and diodes, is rather cheaper than a 200A one.

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  • \$\begingroup\$ As @Neil_UK understands, not only 200A output, but 10% Vac ripple over DC unregulated implies 10X pulse charge current or 2kA. THis is why SMPS are more efficient and active PFC mandatory now for large power supplies draw clean Sine current. It's not always about what the load needs, rather what current THD is generated and when many , harms source power grid components. \$\endgroup\$ Commented Jul 12, 2017 at 14:55

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