Power Supply From Old PSU





Introduction: Power Supply From Old PSU

In this instructable, i tried to explain how to make a desktop power supply from an old PSU with minimal cost. Most of the materials i use are parts that can be easily found or salvaged from broken or scrapped electronic instruments.

The reason for the selection of PSU is that it provides stable voltage-current and also it is free.

At first we decide what we need and start collecting materials. In my projects, generally i need 12V, 5V and 3V. Because of this i did not add variable voltage, voltage screen or other outputs on the PSU (-12V) etc.

I planned to avoid the time losses in future projects by taking different outputs (USB, Banana jack, spring loaded wire terminals) for 12V and 5V. For 3.3V, I only got the banana jack output.

Step 1: Getting Started

First of all, it is necessary to pay attention to safety because of strong capacitors in PSU. The energy hidden in it can be really annoying. Secondly, make sure that the cables are not plugged in during operation. Everyone is responsible for their own safety.


  • 1 x PSU
  • 1 x On / off button
  • 1 x spring loaded double wire terminals
  • 2 x Female USB jack
  • 4 x Banana jack
  • Soldering Iron
  • Drill
  • Rasp
  • Screwdriver
  • Cable stripper-cutter
  • Hot Glue
  • X-Acto Knife
  • Spray Paint
  • Rotary Tool

If there is a label on the PSU, it can save time to note the color and voltage of the cables. In this case, i need the orange (3.3V), red (5V) and yellow or yellow/black (12V) cables.

Step 2: Opening Up and Planning

Let's open the case and get rid of the wire collectors, jacks etc. on the cables. Group the orange, red, yellow and black wires. We also need to green cable here as well to operate the PSU. Apart from these, we can cut other cables. Make the estimated placement of the sockets and mark the places will cut and drill, according to their dimensions.

Step 3: Cutting the Case

Cut and drill the marked places with the rotary tool. For USB sockets, we first drill holes and then rasp them to the size desired. If possible, it should be done this after completely removing the circuit board for without spilling metal shavings on the circuit board. This eliminates the possibility of damaging any cable or component.

Step 4: Customization

At this stage we add a little visuality to the power supply case. This step can be passed. After completely dismounting the case, i painted the bottom part black and the upper part yellow with spray paint and then left it dry. Then i got the printout the shape, i cut it and glued on the case and painted it again with black spray paint. After dried, carefully remove the templates.

Step 5: Wiring the On/off Button

It came up to connect wires. First we will connect the button that will allow us to turn on and off the power supply. Generally, PSUs can not be turned on when not connected to the computer motherboard. For this we need to connect green cable that we have previously reserved, and any of the black cables (GND). So we will be able to turn on and off the power supply without needing a computer. Green cable is soldered to one leg, and black cable is soldered to the other leg. I salvaged the button from an old broken extension cable.

Step 6: Wiring the USB's

After soldering the button, we cut the black, yellow, orange, and red cables in the appropriate lengths. After inserting the USB sockets, place one black cable together with red (5V) and yellow (12V) cables in the same way as in the picture. Fixed with hot glue to keep them in their places. I also salvaged these USB jacks from old burned phone chargers.

Step 7: Wiring the Banana Jacks and Spring Wire Terminals

For banana jacks and spring wire terminals, we group each cable in pairs. After putting the banana jacks together with the insulators in the openings we opened in the case before, we connect the cables in the order we want. Then we solder the yellow and red wires to the spring loaded wire terminal with black (GND) cables. In the images above you can see where I salvaged the spring loaded wire terminal. In this project, the only parts I bought were banana jacks.

Step 8: Testing

After connecting all the cables and putting the sockets in place, we do checks before closing the case. I already closed up the case before the checking but thankfully there is no problem about wiring. After the checking, i added labels on each socket.

Thank you for reading, if you like please vote.

PS: Sorry for my english :)

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46 Discussions

Very well done Instructable! Thank you for sharing it with us!!

English is very, very good for a non-native speaker. I've spent much
time over many years trying to learn German and Spanish and could not do
as well in either language as you did in English.

I've seen
articles on converting old PSUs to test bench supplies. All use the
standard +12V, +5V, and +3.3 V outputs used by most computers. I would
like to have also a 110-120VAC output. I could then plug my soldering
iron into the bench supply instead of having to find another workshop AC
outlet. It would, I think, reduce bench clutter some, too.

that such a modification is possible, how would you go about adding a
110-120VAC output? I realize I would need a female receptacle installed
in the case; but, being a real electronics newbie, I don't know how to
go about it. Would it be as simple as connecting from male input
receptacle pins or wires to the new female receptacle?

I'm considering for this project has an O/I switch beside the 110-120
VAC input receptacle. I think this would prevent power to the PSU in
the O position and allow power in the I position; so this leads me to
think that I might be able to wire from the switch to the female
receptacle. How would I be able to determine if the switch can handle
the pass through load for both the PSU and the output 110-120 VAC?

Again, thank you for this 'ible!!!


6 months ago

Sorry if this is a stupid question, can you connect to +12V and -12V to effectively give you 24V ?

Need to make one
For a car stereo in the shed
Hope he holds the amps
Love the instructions

That is a really nice design. Good work.

Thanks a lot for your tutorial, it's great and your English it's mutch better than mine.

1 reply

1 year ago

Nice job, I've got several projects that could do with this to power them, voted up ! :-)

1 reply

Nice warning labels!

One silly question:

Why waste paint on the whole cover when doing just the top would be sufficient to apply those stencils?

1 reply

:) At first I wanted to paint in black and yellow. But then i did not like the yellow and decided to make it completely black. The idea to apply these labels, came to my mind just before applying black paint.


1 year ago


A couple of notes, covered in other instructables of converting old AT supplies to Bench supplies:

#1, IF the supply has been in use within at least an hour before mod, Assume the HV Capacitors as still charged! (read 110-200V Possible) apply a load across the +5 & +12, and wait that hour! Never rely on the discharge resistors to be functioning!

#2, If the supply doesn't power-up with the Mains switch, make sure the green Pwr_On wire of the main board connecter is shorted to GND.

#2A, IF the supply powers-up for only a few seconds, then powers-down on it's own, apply a load to +5 & +12.. IF it stays running with this load, but shuts-down without it, apply a 33-Ohm 5W (I've seen 10-Ohm, 10-Watt, but seemed kinda low) resistor across +5 to GND.

4 replies

Also, on some of the older supplies that had it, the white wire of the main connector, was actually -5V (Some older dynamic memory used it.), but newer supplies rarely have this included.

Yeah, but they often have something more useful, a second 12V rail!

Hi Gelfling6,

All good, just a little friendly nitpicking...

You already know this stuff but others may not be so experienced.

#2. The black wires are not really GND.

Ground is the chassis, through the thicker green wire on the MAINS connector.

In the interest of clarity, I recommend using 0V or Black Wire when referring to it.

#2A. I have read many instructables that say the load need only be on the rail with the highest current limit. No harm in using it on both, but if the maker has only one, he doesn't need to put off building this to wait for snail-mail from China. ;-)


Good question, chargerR!

It depends on your PSU. Everything you need to know is on that label...

Important: You cannot have all rails at max current. The label has the wattage, too. That and the voltages you will be using at any given time will let you calculate what you can expect from the unit you have.


Great project! We all have a pile of these around. I'm doing a project with a bunch of PS that are in the middle of a cord (not "wall wart", but like a snake that had lunch!), to do the same thing. I would really be interested in how much (AC) current your PS draws when there is no load. There are newer kinds that shut down with no load (as mentioned in comments), but I have some REALLY old ones(!).

Right now, I am choosing the banana chassis connectors, and I couldn't help notice that you had only included a single ground (where the bananas are). I often need more than one voltage at a time, so I might want a 'pair' of + and - for each voltage. That takes a lot more room, though...

Your English is perfect!

Thank you for sharing!

1 reply

Unfortunately I can not say it because I do not have equipment for the measure AC current.

Beginning of the project i was think to add GND output for 5V and 3V, too. But there was not much space, so i add only one to banana jack section.

Thanks for the nice comments and i wish success to you on your project :)