Each PSU Cable Meaning: ATX, CPU, PCIe, SATA, Molex Explained

Quick answer: what each PSU cable means

The “meaning” of each PSU cable is the component it powers and the connector standard it follows. In a typical PC: the 24-pin ATX powers the motherboard, the 4+4 (8-pin) EPS/CPU powers the CPU, the 6+2 PCIe powers GPUs and some add-in cards, and SATA or 4-pin Molex powers drives and accessories.

The safest rule is simple: plug PSU cables only where they are labeled for that exact purpose (CPU to CPU/EPS, PCIe to GPU/PCIe, SATA to SATA devices), and never mix modular cables across PSU brands/models.

PSU cable cheat sheet

Use this table to identify each cable by connector shape, label, and typical use. Always check the PSU-side label (especially on modular units).

If your PSU is modular, the motherboard-side connectors are standardized, but the PSU-side pinout is not. That is the main reason modular cable mix-ups can destroy hardware.

24-pin ATX motherboard cable: what it does

The 24-pin ATX (often a 20+4 split plug) is the primary feed for the motherboard. It carries multiple voltage rails and control lines: 3.3V, 5V, 12V, standby power, and signaling such as “power on” and “power good.”

How to recognize it

• It is the largest connector bundle from the PSU, usually sleeved together and labeled MB or ATX.
• It plugs into the long socket on the motherboard edge (commonly right side of the board).
• The 4-pin “+4” segment snaps to the 20-pin portion to form 24 pins.

Practical note

A system may power on with only the 24-pin connected, but it will typically fail to boot because the CPU power connector is separate (EPS/CPU).

CPU power cable: 4-pin and 8-pin EPS (4+4)

The EPS/CPU connector feeds 12V to the motherboard’s CPU voltage regulation (VRM), which then steps it down for the processor. Many boards use one 8-pin; some add a second 4-pin or 8-pin for heavy overclocking or high-core-count CPUs.

Meaning of “4+4”

“4+4” means the plug splits into two 4-pin halves so it can fit either a 4-pin CPU header (older/entry boards) or an 8-pin CPU header (most modern boards).

Common mistakes

• Confusing EPS (CPU) with PCIe (GPU): both can be 8-pin, but they are keyed differently and wired differently.
• Plugging a “fits with force” connector: if it does not seat easily with the latch aligned, it is likely the wrong cable.

If a PC powers on for a second and then shuts off, or spins fans but shows no POST, an unplugged or incorrect EPS/CPU connection is a frequent cause.

GPU power cable: PCIe 6-pin, 8-pin (6+2), and 16-pin

PCIe power cables are designed for graphics cards and other PCIe devices that draw more power than the motherboard slot can safely provide. A PCIe x16 slot can supply up to 75W by design; external PCIe power adds additional headroom.

PCIe 6-pin vs 8-pin: what the numbers imply

• PCIe 6-pin is commonly associated with up to 75W from the connector.
• PCIe 8-pin (6+2) is commonly associated with up to 150W from the connector.
• A GPU with two 8-pin connectors is often designed around a power envelope near 75W + 150W + 150W = 375W (slot + two cables), though real behavior varies by card BIOS and transient spikes.

16-pin GPU connectors (12VHPWR / 12V-2x6)

Some modern GPUs use a 16-pin connector. Its “meaning” is still GPU power, but it consolidates delivery into a single plug. The key practical requirement is mechanical: fully insert the connector until it is flush and latched, and avoid tight cable bends immediately at the plug to reduce overheating risk.

Best practice for multi-connector GPUs

1. Use separate PCIe cables from the PSU when the GPU has two or more power sockets, unless your PSU manual explicitly states the cable is rated for the combined load.
2. Avoid chaining high-draw GPUs from a single daisy-chain lead if your card regularly pulls hundreds of watts.
3. If you must use an adapter, use the one supplied by the GPU vendor and keep the total cable path neat and strain-free.

SATA power cable: what it powers and why it looks flat

SATA power (15-pin, thin and flat) powers SATA SSDs, HDDs, and many modern accessories (fan hubs, RGB controllers, some AIO coolers). It can carry 3.3V, 5V, and 12V on the same connector, which is why it has more pins than older peripheral connectors.

Practical cautions with SATA

• Avoid powering high-current devices through flimsy SATA-to-other adapters (for example, SATA-to-PCIe for GPUs). SATA power was not designed for GPU-level current.
• Prefer direct PSU cables for controllers and pumps when available; minimize stacked adapters because each contact adds resistance and heat.
• If a drive intermittently disappears, reseat the SATA power connector and check for loose-fit plugs on multi-drive daisy chains.

Molex (4-pin peripheral) cable: when it is still useful

The 4-pin “Molex” peripheral connector is older but still common on accessories: case fans, fan controllers, LED strips, some pumps, and legacy drives. It provides 5V and 12V with two ground pins.

Pros and cons in real builds

• Useful for accessories that do not need motherboard control (simple fan hubs, basic lighting).
• Can be physically stiff; partial insertion increases resistance and heat—push until fully seated.
• Cheap Molex adapters are a common failure point; use high-quality parts if powering anything mission-critical (e.g., a pump).

Small/rare PSU connectors: Berg (floppy) and fan/RGB power

Some PSUs include a small 4-pin Berg connector (often called “floppy power”). It is uncommon in modern PCs but may appear on accessory chains.

Important distinction: PSU power vs motherboard headers

Fans and RGB lighting are often controlled by the motherboard, but powered in two different ways: motherboard headers provide control signals (PWM/ARGB), while the PSU provides bulk power (SATA/Molex) to hubs and controllers. Do not confuse RGB connectors with PSU cables; they are not interchangeable.

Modular PSU cables: what the PSU-side connector means

On modular and semi-modular PSUs, one end of the cable plugs into the PSU body. That PSU-side connector is where most confusion happens: it is not universally standardized, even if the component-side end (ATX/EPS/PCIe/SATA) is.

Practical rule that prevents expensive mistakes

Only use the modular cables that shipped with your exact PSU model (or official replacements for that model). Swapping “similar-looking” cables between brands can send the wrong voltage to pins and permanently damage the motherboard, GPU, drives, or all of them.

Label reading checklist

• PSU port labels: MB, CPU, PCI-E, SATA/PERIPH
• Cable labels near the connector (often printed on heatshrink): CPU vs PCI-E
• Connector keying: the squared/rounded pin shapes should align without force

Troubleshooting by cable symptoms

When a cable is missing, incorrect, or overloaded, the PC often provides consistent clues. The checklist below ties common symptoms to PSU cables.

If you suspect a modular cable mismatch, stop powering the system until you confirm every cable belongs to that exact PSU model.

Safe wiring habits that matter in practice

PSU cables are simple, but the consequences of one wrong connection can be severe. The habits below eliminate most real-world failures.

• Match labels: CPU/EPS cable to CPU header; PCI-E cable to GPU; SATA to SATA devices.
• Seat connectors fully: latches engaged, no visible gap, no sideways stress.
• Distribute load: high-draw GPUs are better served by multiple separate PCIe leads than one daisy chain.
• Avoid risky adapters: especially SATA-to-PCIe for GPUs or other high-current loads.
• Modular discipline: never mix modular cables across PSU models, even within the same brand unless explicitly stated compatible.

Conclusion: the meaning of each PSU cable in one line

24-pin ATX = motherboard, 4+4 EPS = CPU, 6+2 PCIe or 16-pin = GPU, SATA/Molex = drives and accessories. If you follow the labels, avoid modular cable mixing, and do not rely on unsafe adapters, you will prevent the most common PSU-cable failures.