To tie two PSU together for additive power in a single PC, you connect the primary power supply to your motherboard and use a dual-PSU adapter or relay switch to trigger the secondary unit when the system powers on. This method lets you combine the wattage of two standard ATX power supplies to run multiple GPUs, mining rigs, or other high-draw components that exceed a single unit's capacity.
What does “how to tie two PSU together” actually mean?
When someone searches for how to tie two PSU together, they usually fall into one of two camps. The first is a consumer PC builder who wants to add the wattage of two standard ATX power supplies together, say, a 750W unit plus a 650W unit to get roughly 1400W of combined capacity for multiple graphics cards or a crypto mining rig. The second is an IT administrator working on enterprise hardware like an HPE or Fortinet server, where “tying two PSUs together” means installing a second hot-swap unit for 1+1 redundancy, so if one fails, the other keeps the system running without interruption. This guide focuses on the first scenario: combining two consumer ATX PSUs for additive power in a single PC. If you need server-style redundancy, skip to the final section of this article.
Why combine two power supplies for more wattage?
Single PSUs top out at around 1600W for most consumer models, but high-end gaming rigs with dual or triple GPUs, heavily overclocked CPUs, and multiple water pumps can easily exceed that. Crypto mining rigs are the most common example, they often run six or more graphics cards at full load, drawing 100W or more per GPU. A single 1200W unit might not be enough, and buying a single 2000W+ server PSU is expensive and may not fit in a standard ATX case. Tying two PSUs together lets you use affordable, readily available units to reach the combined wattage you need. It also provides flexibility: you can run the primary PSU for the motherboard and CPU, while the secondary PSU powers only the GPUs or other peripherals. This approach is popular in mining rigs and multi-GPU workstations where a single unit's wattage is simply insufficient.
Critical safety warning: never use a simple splitter cable
You might be tempted to just split the 24-pin ATX connector from your motherboard to both PSUs using a Y-cable. Do not do this. Directly connecting the +5V or +12V outputs of two independent PSUs can cause voltage feedback, where one PSU tries to backfeed into the other. This can damage both units, your motherboard, and connected components, and in extreme cases, it can start a fire. The correct way to tie two PSUs together is with a purpose-built dual-PSU adapter or a power supply sharing switch. These devices use a relay or MOSFET circuit to isolate the secondary PSU's outputs until the primary PSU has stabilized. The adapter connects to the primary PSU's 24-pin ATX connector (or a dedicated trigger wire) and sends a signal to the secondary PSU to turn on. This ensures the secondary PSU only powers up after the primary is running, preventing any dangerous feedback loops.
What you need before you start
Before you begin, gather the following items:
- Two compatible ATX PSUs, They should have matching voltage outputs (all modern ATX PSUs use +3.3V, +5V, +12V) and the necessary connectors for your components. Ideally, use units from the same brand or at least with similar voltage regulation specs.
- A dual-PSU adapter or relay switch, This is the critical safety component. Look for one that supports the wattage of your secondary PSU and has the correct connectors (usually a 24-pin pass-through for the primary and a separate 24-pin or 20-pin trigger for the secondary).
- Screwdriver, For mounting the PSUs and securing cables.
- Cable ties or Velcro straps, For managing the extra cables and keeping them away from fans and moving parts.
- Anti-static wrist strap (optional but recommended), To protect your components from electrostatic discharge while you work.
You may also want to check the user manuals for both PSUs to confirm their connector layouts and any specific linking instructions.
Step-by-step: how to tie two PSU together for additive power
Follow these steps carefully. Always work with the system unplugged from the wall.
1) Power off and ground yourself. Unplug the PC from the wall outlet, switch off both PSUs, and wait at least 30 seconds for capacitors to discharge. Wear an anti-static wrist strap or touch a grounded metal object before handling components.
2) Mount both PSUs. Install the primary PSU in the standard ATX bay in your case. If your case has a second PSU bay (common in mining cases), mount the secondary PSU there. If not, you may need to mount it externally or use a bracket. Ensure both PSUs have their fans facing outward for proper airflow.
3) Connect the primary PSU to the motherboard. Plug the primary PSU's 24-pin ATX cable and 8-pin CPU cable into the motherboard as you normally would. Do not connect the secondary PSU to the motherboard at this point.
4) Connect the dual-PSU adapter to both PSUs. Take the adapter's main cable and plug it into the primary PSU's 24-pin ATX connector (the one that goes to the motherboard). The adapter will have a pass-through connector that still allows the primary PSU to power the motherboard. Then, connect the adapter's secondary trigger cable to the secondary PSU's 24-pin ATX connector. Some adapters use a separate 20-pin or 4-pin connector for the secondary, follow the adapter's instructions.
5) Connect the secondary PSU to GPUs/peripherals. Plug the secondary PSU's PCIe power cables into your graphics cards, and its SATA or Molex cables into storage drives or other peripherals. Do not connect the secondary PSU to the motherboard's CPU or 24-pin connectors, it should only power add-on devices.
6) Manage cables. Use cable ties to bundle the extra wires and route them away from fans, heatsinks, and sharp edges. Ensure no cables are pinched or strained. Good cable management also improves airflow, which is critical because two PSUs generate more heat.
7) Power on and test. Plug both PSUs into the wall (ideally into the same surge protector). Switch on the primary PSU first, then the secondary. Press the power button on your case. The secondary PSU should turn on automatically via the adapter's relay. If nothing happens, see the troubleshooting section below.
Testing and troubleshooting your dual-PSU setup
Once everything is connected, verify both PSUs are working. The primary PSU's fan should spin, and the secondary PSU's fan should also spin up when the system powers on. Check that the motherboard, CPU, GPU, and all peripherals are receiving power. To confirm the secondary PSU is delivering power to your GPUs, you can use software like GPU-Z to monitor the +12V rail voltage, it should stay stable under load. If you want to test the secondary PSU independently before installing it, you can use a paperclip to jump the green wire and a ground wire on its 24-pin connector, this is the classic trick to "power up PSU without motherboard". However, never do this while the PSU is connected to your system.
Common issues and fixes:
- Secondary PSU doesn't turn on: Check that the adapter's trigger cable is firmly connected to both PSUs. Ensure the secondary PSU's power switch is set to "1" (on). Some adapters require the primary PSU to be under a minimum load before the relay activates, try connecting a fan or a small load to the primary PSU.
- System won't boot: Make sure the primary PSU is connected to the motherboard's 24-pin and CPU connectors. If you accidentally connected the secondary PSU to the motherboard, disconnect it immediately.
- Random shutdowns under load: This usually means the combined wattage is insufficient or one PSU is faulty. Calculate your total power draw and ensure it's below the combined capacity. Also, check that both PSUs are plugged into the same wall circuit to avoid ground loops.
- GPU not getting enough power: If a graphics card isn't receiving enough power, it may crash or show artifacts. Use a tool like GPU-Z to check the +12V rail voltage. If it drops below 11.4V, your secondary PSU may be too weak or faulty. You can also "check if GPU is getting enough power" by swapping the PCIe cables from the secondary PSU to the primary PSU (if the primary has spare connectors) to isolate the issue.
A note on enterprise server redundancy
If you're working with enterprise servers from HPE, Dell, or Fortinet, “tying two PSUs together” means something entirely different. In these systems, you install a second hot-swap power supply unit into a redundant bay (for example, the FortiPAM 400G ships in a single 1+0 configuration, and you can add a second PSU to enable 1+1 redundancy). In 1+1 redundancy, the server continues to operate if one PSU fails. This is not additive power, the server draws from both PSUs simultaneously but each PSU is rated to handle the full load alone. The goal is fault tolerance, not increased wattage. For HPE systems, you may need a dual-slot power supply adapter to install two flex slot PSUs into a single bay. Always consult your server's hardware manual for specific installation steps, as the process involves hot-swap bays and specific redundancy policies (like 2+2 or 3+1) that dictate how many PSUs can fail before the system shuts down. If you need additive power for a server, you should upgrade to a higher-wattage single PSU or use a dedicated parallel operation controller, never attempt to tie two standard ATX PSUs together in a server chassis.
