Introduction: Power Supply From Old PSU

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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 :)


phoe (author)2018-01-11

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

PascalS22 (author)2017-07-14

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

kadirkizli (author)2017-06-30

That is a really nice design. Good work.

gbonilla1 (author)2017-06-08

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

punisher_1211 (author)gbonilla12017-06-12

Thank you :)

phoe (author)2017-06-06

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

punisher_1211 (author)phoe2017-06-12

Thanks :)

RobertC2 (author)2017-06-10

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?

punisher_1211 (author)RobertC22017-06-12

:) 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.

kyleyt (author)2017-06-11


Gelfling6 (author)2017-06-02

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.

Gelfling6 (author)Gelfling62017-06-02

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.

RobertC2 (author)Gelfling62017-06-10

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

RobertC2 (author)Gelfling62017-06-10

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. ;-)


punisher_1211 (author)Gelfling62017-06-03

These are good details and informations. Thank you

WilliamK31 (author)2017-06-04

can the 5v & 3v outputs be put in series with the 12v line for higher voltage?

RobertC2 made it! (author)WilliamK312017-06-10

No. Since they use the same ground you cannot do that. You can get up to 24v out of most of these by using -12v (blue wire) as negative, and +12v (yellow wire) as your positive. But, as stated in another comment, the max current will be the lesser of the two limits. So, around one amp, usually.

There are many combinations to make different voltages... The black wires are not actually Ground. They are the 0 volt reference for the other voltages. The voltages you get are the differences between the two rails you use. Always use the higher voltage rail as the positive, and remember that your maximum current limit is the weaker of the two rails you are using. In the top right corner of this photo is a list of possible voltages. (That is the face plate for the one I made a couple years ago.)

punisher_1211 (author)WilliamK312017-06-05

If the goal is to get a high voltage, i think it can be done by using -12V as GND with 3V or 5V. But then the current will very low. (In my PSU, current will down to 0.8A. Because i can get max 0.8A from -12V output) But I'm not quite sure.

chjm1 (author)WilliamK312017-06-05

You should not try this as the ground (to
which every Voltage is compared to) is common for all the outputs. Then you will be, in a very simplify explanation, short-cutting the
higher voltage through the lower voltages.

Putting several power
supplies in series to get more voltage only works when you have
individual power sources not sharing the same ground, i.e.: batteries.

Hope it helps.

TechnicalKid (author)WilliamK312017-06-05

No, all the voltages have the same ground potential, if you try to wire them in series you effectively short them out.

changerR (author)2017-06-05

how much power can it supply?

RobertC2 (author)changerR2017-06-10

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.

OptimisticPessimist (author)2017-06-05


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!

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 :)

OctavioB (author)2017-06-05

I like it... in fact I had the same concept in mind but really didn't devote anytime into the conversion. You did it perfectly. Thanks a ton bud!

punisher_1211 (author)OctavioB2017-06-05

Thanks :)

Ancient1 (author)2017-06-04

I think that using USB socket for 12V is dangerous.

1. Can easily be mistaken for 5V USB

2. USB wires are not rated for the current and can overheat.

punisher_1211 (author)Ancient12017-06-05

Thanks but i sticked labels above them to avoid mixing and generally i need low currents when work with usb's.

blackICE19240 (author)Ancient12017-06-04

Im pretty sure there is no use for a 12v usb but extra current can only be useful for the 5v

VincentT57 (author)blackICE192402017-06-05

I think "Ancient1" means you MUST NOT make any USB output with 12V at all. It makes no sense! Just remove yellow and put red wire. :)

ZulkifliN (author)2017-06-05

It is a very useful project. Kudos to you my friend.

punisher_1211 (author)ZulkifliN2017-06-05

Thank you

morphman001 (author)2017-06-05

This is a cool project!

Im going to make this. well done


CPUDOCTHE1. (author)2017-06-04

I would MUCH rather hook the green power on wire to ground and put the switch in Line wire from the 120V connector going to the board so there was no 120V present on the board when the switch is OFF.

That is good idea, i might be considered to revision on the button. Thanks

SteveJ25 (author)2017-06-04

not a good idea unless you replace all the capacitors. made in china means chinese junk capacitors that age like bananas

preschau (author)2017-06-04

You are right, having a USB connector supplying 12 volts is a disaster waiting to happen.

arvevans (author)2017-06-04

It is very possible to adjust the +12 volt output to be a more conventional 13.6 volts. The internal regulator circuitry uses 3 resistors, one from 12V, one from 5V connecting to one going to ground. The resistor going to the 12V can be changed slightly so that the 12V output will increase to 13.6. However, this is not all that happens. The internal PWM signal controls both 12V and 5V output. If you raise the +12V the 5V will also be affected.

e5frog (author)2017-06-04

These PSU:s often require a load to make them start and keep a proper voltage, a low ohm high watt resistor between 5V and ground (or 12V).
The power on signal usually only needs an impulse to start, almost any low voltage push button would work. The larger button in the instructable could probably be used to turn mains on/off.

KB0LFL (author)2017-06-04

Thank you so much for the directions. Would it be possible to adjust the 12v output to 13.8v?

DhanyS (author)2017-06-04

Nice rig, power supply from pc PSU.

russ_hensel (author)2017-06-03

Welcome to the club: Just a note to let you know I have added this instructable to the collection: Encyclopedia of ATX to Bench Power Supply Conversion


Take a look at about 70 different approaches to this project. This topic is one of the more popular of all instructables.

Thank you for adding this instructable. I think there is a problem with the link, but I found it anyway.

I wish I'd seen it before. It's good that they all gather in one place.

饼干 (author)2017-06-02


Gelfling6 (author)饼干2017-06-02

待机通常是+5 ...这是由电脑的瞬时接触开关来切换Pwr_On到GND ...


Standby usually is +5... this is used by the computer's momentary contact switch to toggle the Pwr_On to GND...

Swansong (author)2017-06-01

That looks good, great way to reuse it :)

punisher_1211 (author)Swansong2017-06-01

Thank you :)

RushFan (author)2017-06-01

Very nice! Great job.

punisher_1211 (author)RushFan2017-06-01

Thanks :)

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