alt Hacker NewsOnly partially true.
In well-designed microelectronics, they will.
The standard circuit involves a fuse, a fast Zener clamp, and sometimes a small resistor (e.g. 1 ohm) and/or capacitor. The design parameter is that, with the current limit from the resistor, the Zener should not blow out before the fuse.
The resistor needs to be small enough to not lose a lot of voltage under normal operations, but to still protect the Zener during the short surge during which the fuse blows. For most microelectronics, that's not hard. A 0.5W USB device might have 100mA of current max, which across 1 ohm is 100mV, so negligible for most purposes.
With high-power devices, it gets more complex.
Of course, consumer devices (a) will never be fixed (b) don't sell on this (c) every penny counts, so there's no market pressure to do things right.
But that's how we used to do it, and how it's still done many places where things count. If I'm building a one-off or few-off, it definitely will have proper protection.
That's a good design for input overvoltage protection (assuming I've drawn the correct schematic in my head). But it doesn't help against most other fault conditions, particularly anything to do with the load/downstream going short.
Really, if you care beyond "blow the fuse if something shorts", you need active current limiting. For common cases like USB ports, you can buy chips that do it cheaply and efficiently. There are also some textbook circuits, though they each have their pros and cons. No matter what, if you've got a pass transistor or switching transistor that's about to go seriously overcurrent, you have to do something about it with active parts -- fuses aren't going to get it done.
But defense in depth is always a good strategy, and fuses play a key role there. The active circuitry saves the rest of the design; if it can't get the job done, the fuse makes sure nothing burns.