Hi,

Most likely, there's a switch under the sticker. This was quite common for AT and early ATX PSUs.

The only way to be sure about it is to open the PSU and check its layout between the bridge rectifier and the switching transistors. If there's only a couple of capacitors, then, there's no PFC. But if there is a small capacitor, a small IC, a beefy transistor (or 2/4 transistors), a diode (or 2/none), a big inductor/transformer and a capacitor (boost or flybakc), there can be a PFC circuit.

If tyou really want to add a PFC on your AT PSU, you can still find PFC separate boards that gets 80-260V AC and outputs 330-450V DC and would work with minor modifications (be careful with caps voltage ratings).
This was quite common on ATX PSUs for the years 2000-2004 (when PFC began to be mandatory in Europe for >75W devices).

Jade Falcon wrote:

I found this cheap psu and it has no 110v-240v switch but a sticker like you see on newer psu with active pfc. […]
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I found this cheap psu and it has no 110v-240v switch but a sticker like you see on newer psu with active pfc.

Anyone see this on such an old psu before?

Edit.
Or maybe it can output 240? The arrow is tripping me up.

I am sure it will output whatever goes in.
Most likely there is no switch (why cover it with sticker so nobody can use it?) and it will automatically adjust itself according to input voltage.
I know these things usually have voltage select switch or they are fixed to one voltage range, but it's also possible it works with anything between 100 and 240 volts.
But because it consumes different amount of amps with different voltage input, they just have to label them both.

There is no switch under the sticket

Jepael wrote:

Most likely there is no switch (why cover it with sticker so nobody can use it?)

Because some consumers are idiots and will switch it no matter what, and then complain to the manufacturer that their computer "malfunctioned". The results of this are worse in a country with a higher voltage because the power supply will likely blow, possibly taking the computer itself with it (of course not a problem if there's a fuse in the power supply...).

customers + pupils

yawetaG wrote:

The results of this are worse in a country with a higher voltage because the power supply will likely blow, possibly taking the computer itself with it (of course not a problem if there's a fuse in the power supply...).

Repeat after me: 'Fuses do not protect against over current or over voltage. Fuses are thermal protection only.'

gdjacobs wrote:

yawetaG wrote:

The results of this are worse in a country with a higher voltage because the power supply will likely blow, possibly taking the computer itself with it (of course not a problem if there's a fuse in the power supply...).

Repeat after me: 'Fuses do not protect against over current or over voltage. Fuses are thermal protection only.'

Wikipedia disagrees with you: https://en.wikipedia.org/wiki/Fuse_(electrical)

(and so does my Oxford dictionary)

yawetaG wrote:

(and so does my Oxford dictionary)

while thats true

in practice its the piece of the circuit that gives out first by virtue of it melting.

if everything else in the circuit is less sensitive to the condition that made it blow then it will have saved everything

electronics within a pc however is quite likely to be damaged faster than the fuse will blow if a faulty/incorrectly switched PSU delivers 20 volts down the 12 volt line.

great for not having the pc burn your house to the ground if a short occurs though

Precisely, fuses don't limit the amount of current in a circuit, they have an I^2 t curve (i.e. energy) which roughly conforms with the way in which the fuse melts. Downstream devices must withstand the energy they'll be exposed to while the fuse melts and extinguishes any residual arc. If not, they will fail.

Higher circuit currents will shorten the melt duration (but not necessarily the time for the arc to clear). The circuit will still conduct excess current while the fuse is intact.

There are current limiting fuses and circuit breakers, but even they function quite differently from what you're thinking of.