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To install a power supply, switch it off and unplug it, plug the modular cables into the PSU first, slide the unit into the case bay with the fan facing a vent, fasten it with four screws, then connect the 24-pin motherboard cable, the CPU EPS cable, the graphics card cables, and storage power before you plug in the wall cord. Use only the cables made for that exact power supply model.
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Before You Start
Prerequisites
- A power supply with enough wattage and the right connectors for your CPU and graphics card. The GPU maker lists a recommended PSU wattage and connector type on its specification page.
- A Phillips screwdriver and the four mounting screws that came with the PSU or case.
- The cables that shipped with that specific PSU, plus cable ties or Velcro straps.
- Your motherboard and GPU manuals, which show where each power connector goes.
Know Your PSU Type
A fully modular PSU has no cables attached, so you plug in only those you need. A semi-modular unit has some cables attached, usually the 24-pin and CPU cables. A non-modular unit has every cable fixed. Maker guides from Corsair, NZXT, and Cooler Master all point to the same advice: with modular units, attach the cables to the PSU before you mount it, because the sockets are hard to reach afterward in a tight case.
Safety First
Turn the PSU switch off and unplug the cord from the wall before you handle any cable. Never open a power supply; it holds capacitors that can retain a charge and has no user-serviceable parts. If you use a graphics card with the 12VHPWR or 12V-2×6 connector, follow the GPU and PSU maker guidance, push the connector in fully and evenly, avoid sharp bends right at the plug, and stop using it if you notice heat damage or discoloration.
Quick-Reference Table
| Connector | Where it goes | Notes |
|---|---|---|
| 24-pin ATX | Large socket on the edge of the motherboard | Main power; keyed, press until the latch clicks |
| CPU EPS 8-pin (or 4+4) | Socket near the CPU, usually top left | Labeled CPU; do not use a PCIe cable here |
| PCIe 6+2-pin | Graphics card power sockets | Use separate cables where possible for high-power cards, following GPU guidance |
| 12V-2×6 / 12VHPWR | Graphics card 16-pin socket | Seat fully; avoid tight bends near the plug |
| SATA power | SSDs, hard drives, some RGB hubs | L-shaped keying |
| Molex 4-pin | Older accessories and fan hubs | Only if needed |
| AC power cord | Back of the PSU to the wall | Connect last, switch on after final check |
Step-by-Step Installation
- Prepare the case. Remove the side panels and clear the PSU bay, normally at the bottom rear. If you are replacing a PSU, shut down fully, switch off the old one, unplug the cord, and disconnect its cables from every component before removing four screws on the rear.
- Work out the fan direction. Many cases have a ventilated bottom with a dust filter. In that case, mount the PSU with its fan facing down. If the case has no bottom vent, face the fan up into the case instead. Read the case manual if unsure.
- Attach the modular cables. At minimum, connect the 24-pin motherboard cable, the CPU EPS cable, and the PCIe cables for the GPU. Check both ends: modular cables usually have different connectors on each side, and the PSU end is labeled. Do not mix cables from other makers or other PSU models, because pin layouts can differ and mismatched cables can damage components.
- Slide the PSU into the bay. Orient it so the power inlet and switch face the rear panel opening and the screw holes line up.
- Secure it. Fit four screws through the rear bracket. Snug them in an alternating pattern. Do not overtighten.
- Route the 24-pin cable. Pass the cable behind the motherboard tray if the case allows, bring it to the large socket on the board’s edge, and push until the latch clicks. Alignment matters; the connector is keyed so it only goes in one way.
- Connect the CPU power. Route the CPU EPS cable through the top rear cutout to the 8-pin or 4+4-pin socket near the CPU. Some boards have two sockets; the manual says whether both are required. Make sure the cable is labeled for the CPU, since PCIe cables can look similar.
- Connect the graphics card. Plug in the number of PCIe cables the GPU maker lists. For 12V-2×6, press the connector fully until it is flush, and keep a gentle curve in the cable. Use the cable that came with your PSU or the adapter that came with the GPU, according to the maker’s guidance.
- Connect storage and extras. Plug SATA power into drives and any accessories. Leave unused modular cables out of the case and store them in a bag for future upgrades.
- Tidy and inspect. Use Velcro or ties to group cables behind the tray. Keep slack near the connectors so there is no tension, and keep cables away from fan blades. Look at each connector to confirm it is fully seated.
- Power on. Plug the AC cord into the PSU and the wall, flip the PSU switch to the on position, and press the case power button. Watch for fans spinning and a display signal.
What Result to Expect
On first boot you should see the motherboard logo or BIOS screen, with CPU and case fans spinning. The PSU fan may stay still at low load on models with a zero-RPM mode, which is normal; check the maker’s manual. If the PC does not start, switch off and unplug the PSU, then recheck the 24-pin, the CPU EPS, the front-panel power button connection, and the switch on the PSU. Do not force connectors. If you smell burning, see sparks, or hear a pop, switch off at once and contact the PSU maker.
Common Mistakes
- Mounting the PSU with the fan facing a surface with no airflow.
- Using cables from another PSU, even from the same maker.
- Plugging a PCIe cable into the CPU socket because they look alike.
- Partially seated 24-pin or GPU connectors, which cause random shutdowns or no boot.
- Bending a 12V-2×6 cable sharply right at the plug.
- Forgetting to switch the PSU on, or leaving it off at the wall.
- Leaving loose cables where they can contact fans.
When Not to Do It
Do not install or replace a PSU if it is damaged, if you do not know its origin, or if its wattage and connectors do not suit your parts. If you are unsure about wattage, use the GPU and CPU makers’ power guidance. Do not open a PSU to repair it. If a unit trips, smells, or makes unusual noises, contact the maker or a qualified technician.
Frequently Asked Questions
Which way should the PSU fan face?
If the case has a ventilated bottom with a filter, the fan usually faces down to draw cool air from outside. If the bottom is solid, face the fan up into the case. The case manual normally shows the intended orientation.
Can I use cables from an old power supply?
No. Modular PSU cables are not standardized across makers or even across models, and mismatched cables can send power to the wrong pins. Use only the cables that shipped with the PSU, or ones the maker lists as compatible.
Do I need to connect every cable?
No. Connect the 24-pin, the CPU EPS, the GPU power if the card needs it, and power for storage. Unused cables can stay out of the case, which also helps airflow.
How many PCIe cables does my graphics card need?
The GPU maker lists the required power connectors on its specification page. Many high-power cards also state whether to use separate cables for each connector, so follow that guidance rather than guessing.
Why does my PC not turn on after installing the PSU?
Common causes include the PSU switch being off, a loose 24-pin or CPU connector, or a front-panel power button cable that is not connected. Switch off, unplug, and recheck each connection. If the problem persists, contact the PSU maker.
Is it safe to touch the inside of a power supply?
No. Never open a power supply, because internal capacitors can hold a charge even when unplugged. Leave any internal repair to the maker or a qualified technician.
