If you’re tempted to reuse an old modular power supply cable on a new power supply, save yourself a lot of trouble and buy a new one instead. You could wind up completely frying thousands of dollars in components otherwise.
Most Computer Components Are Plug and Play
For the most part, computer components are safe to mix and match as long as they’re designed to fit where you’re trying to use them.
As an example, there isn’t a situation where you’re going to plug a PCIe x4 card intoa PCIe x4 slot or a PCIe x16 slotand have something catch on fire as a result. That generally applies to pretty much any connector you find—if it fits without forcing it, it is probably safe.
There is one notable exception: modular power supply cables.
Mixing Power Supplies Cables Is Not Safe
Modular power supplies have become the norm over the years as people look forways to reduce cable clutter and keep things a bit tidier. More often than not, the modular cables from modular power supplies last far longer than the power supplies they came with, or the computers they once powered.
As a result, people that build their computers tend to have a lot of these things lying around.
By accident or by choice, this sometimes results in a modular cable from one power supply getting plugged into a completely different power supply. And theywillfit, since they share the same physical connector.
The trouble is the electrical output on the power supply side. Despite sharing the same physical connector, the contacts on the power supply side aren’t necessarily the same between different power supplies; wires are sometiems routed to a different location before they’re terminated at the end that connects to your motherboard, GPU, or other component.
In practice, that means you may wind up delivering 12 volts to a pin not designed to handle it, connect a ground to something that is expecting 5 volts, and so on. At best, it won’t work. At worst, it could damage the component, your power supply, or both.
Don’t mix power cables between power supplies, even if they’re from the same manufacturer. They may not be compatible.
Where Do You Get Safe Cables?
The only way to be sure you’re getting a safe cable is to purchase one directly from the manufacturer of your power supply, and you need to be sure you’re buying a replacement for yourexactpower supply.
You cannot assume that just because it comes from the same manufacturer that the cable from one power supply will be compatible with another.
Some manufacturers have convenient sites where you can check:
Can You Check Cables to Ensure They’re Compatible?
Yes, you can, but I always recommend against it. Cables are relatively inexpensive and are usually readily available from PSU manufacturers. If you make a mistake, you could kill a graphics card that costs hundreds of dollars or fry a motherboard. Quite simply, it isn’t worth the risk.
However, if you’re intent on trying, here’s how to do it without cooking anything. There are two different approaches.
Buy a Tester
There are actually PSU testers that can tell you if your cables are working correctly. A cable that isn’t compatible with a power supply will read incorrectly when plugged into a meter. The specific error you get depends on which wire is malfunctioning, but it is the most reliable way to know if a cable won’t work.
Thermaltake Dr. Power III ATX Power Supply Tester
Thermaltake Dr. Power III ATX Power Supply Tester let’s you test most common power connectors found in PCs to determine if your power supply is malfunctioning.
Test a PSU and Cable Manually
If you need to do this manually, without a specialized tester, you’ll need a multimeter, a bit of patience, and a way to trick your power supply into thinking that it has been plugged into a motherboard. Power supplies are smart, and they won’t even turn on unless they detect that they’re connected to a motherboard. Usually that trick involves a short piece of wire, but I’ve used an insulated paperclip before.
Making a mistake here could lead to irreparable damage to your PSU.
Tricking one into turning on used to be as simple as installing a small jumper wire between the green wire and any black wire on the main 24-pin ATX wiring harness, but since power supply cables are now often sheathed or all black wire, it is a bit more complicated.
If you need to do it manually, you’ll need a short length of wire, maybe 3 or 4 inches long. Any gauge between 16 and 20 will work.
The motherboard end of the 24-pin ATX connector will always be the same, so you may figure out what you need to jumper by position (green corresponds to pin 16), but you need to count carefully. This is a diagram of a 24-pin ATX Connector. I’ve marked the pin that needs to be jumpered in green, and marked some commons that will work for a jumper in black. Note the position of the connector clip on the diagram, which I’ve marked in red.
Strip about 1/4 inch off of both ends of a piece of your wire, then connect pin 16 (the green wire) to any of the specified black wires. Your power supply will turn on.
Once that is done, you need to actually measure the voltages at the end of whatever cable you’re interested in. For that, you’ll need to referencethe ATX specification standards. verify to account for the orientation of the connector with respect to how you start counting the pins. The clip that holds the connector in place is always on diagrams and will help you. As a quick example, this is the pin out for a 6-pin PCIe connector.
Assuming you’ve already connected your cable to the modular PSU, all you need to do is set your multimeter to DC Voltage (usually a V without a squiggly line next to it) and check the pins one by one to ensure they read the voltage that they should.
Alternatively, you’re able to test for continuity between either end of the PSU cable to see if they’re connected. If the pin positions on each side of the cable are the same, there can’t be any wires routing from one pin location to another. However, I usually prefer to just hook up a multimeter—it’s a bit of extra work, but I feel more confident seeing the actual voltages.
Given how robust and detailed many PC standards are, it seems strange that industry players have not made any moves to standardize the PSU side of connectors so that this sort of mishap isn’t possible. At a minimum, a universal coding scheme that indicates compatibility would be nice, so we could know if a cable will work without busting out the multimeter.
