Sorry I meant easier to find AC/DC Walmarts.
Well I live in France too, and I can confirm that finding a AC/AC power supply is quite a pain in the neck. Do you have a link or reference for the dual DC wall wart supply you’re using? It might be useful to me 
AC/AC supplies are a little harder to find but I aways find what I need in local electronics shops. These things are heavy and bulky and it makes sense to buy them locally. Ask, and if they don’t have exactly what you need, they will likely order it for you from their suppliers. You will be surprised by how many small companies there are that make that kind of stuff and supply locally.
I recently bought myself one of these AC to DC power modules from Aliexpress with the plan to use it as a bench power supply: https://de.aliexpress.com/item/1005006040723587.html
Unfortunately I can’t get it to work… I tried to power it with two different power adapters (both 12V AC, 800mA) but there isn’t any voltage present at the outputs. Any idea what might be the problem? Did I get something wrong and this module isn’t suitable for this application? 
Schematic:
You need a transformer with 2 different windings and a center tap for ground for this schematic, not the classic AC wall wart with 2 pins for AC.
Where did you connect your power adapter?
You could try to connect you wall wart to one of the 18V inputs and the ground input, and try to adjust the voltages with both pots, but you will never get 15V output with the 12V AC input.
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Looks like a perfectly normal PSU to me. But what sort of power adapter? What this wants is a split transformer with three output leads. A typical wall wart with two leads… if connected to the points marked 0 V and 18 V you’d get half wave rectification so the output would be more ripply than with a split transformer but I’d think you’d get something.
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This is what I suspected… I used a ‘normal’ AC wall wart with 2 Pins and connected the sleeve connection to the ground input and the tip connection to both the AC inputs.
I believed this module was somewhat similar to the Doepfer ‘MNT’ Mini Power Supply or similar products which work with a wall wart like the ones I tried to use.
The output is adjustable and I wanted to use it for ±12V. My 12V AC wall wart actually provides around 14V AC.
My multimeter shows 0V on both the V- and V+ outputs.
I wonder if the circuit can be modified to work with my wall warts?
I had a very similar one and I got it to work with a regular 12V AC wall wart, without a centre tap, and it works fine as a “bench supply” to test modules.
The trick is to connect the wall wart to one AC input and the ground, not the two AC inputs.
Adjust the trimmers accordingly and you will get +/-12V DC at the output. You will be only using half of that bridge rectifier and getting half of the current than you would if you had a centre tap transformer at the input, but then again, the typical supplies that we use in the synths use half wave rectifiers anyway…
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this could work depending on the current your need to draw, the dropout voltage differs between 1.5 and 2.5V depending on the output current:
as @K.ostas wrote: connect to GND and one AC input and play with the pots to get some output. Try to measure the voltages at the inputs of the regulators (pin3) and the outputs of the 4 diodes. After the diodes you should get around 15V DC with an 12VAC power supply.
Check what @Stef said and also check the connections to the wall wart input. In my case, the board it did not initially work because of a wobbly connector!
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That just puts the same voltage on two parallel diodes connecting to the same point, so it shouldn’t alter whether it works or not.
Wall warts are often unregulated, so the voltage varies depending on the load.
If it’s connected to this PSU then the voltage at the inputs to the LM317/LM337 should be roughly about 16 VDC, with a lot of ripple. You could check that with a multimeter. You could also check the resistances, maybe tricky in-circuit but you probably can at least verify they’re in the right ballpark. If so and if there’s a large enough DC input, the regulators should put out a clean voltage which with the pots adjusted to around 2k would be about 12 VDC.
As someone said, check the connections! That’s probably the most likely thing. Otherwise you kind of have two separate circuits here, one for + and one for -, and to have both faulty the same way seems implausible.
I think the LM317 has the same potential problem as the L78L12, where if the output is pulled negative it won’t start up. But if there’s no load connected to the outputs I don’t think that can happen, and in any case it shouldn’t happen to the LM337. So that’s probably not it.
And negative regulators usually need a small load in order to regulate, but they should put out some sort of voltage even if it’s not well regulated, so that’s not likely either. And it shouldn’t affect the positive output. But you could try connecting an LED + resistor from each output to ground anyway. Added: Hm, maybe not adjustables, the resistances probably count as a load…
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You both were right, I used a faulty power connector, which I didn’t realise since the multimeter still showed continuity (go figure).
Now I got an adjustable -12V output, which works fine. The V+ output though only measures 2.5V and the trimpot doesnt do anything. Maybe this part of the circuit is indeed faulty… but I’ll do some more testing.
The voltage to the input of the regulators sits at about ±19V.
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Check the trimpot. I once had a faulty trimpot that didn’t do anything.
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The trimpot seems to work fine. But I took a closer look and found, that one of the resistors on the pcb doesn’t match the schematic. On the LM317 side of the circuit the 220R resistor is actually 1M! I’m pretty sure thats the problem
EDIT: Replaced the 1M resistor with 220R and that actually fixed it! 
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wow good work!! (…)