If you've ever built a PC or upgraded a power supply, you've encountered the dizzying assortment of cables coming out of the PSU. Big black connectors with lots of pins. Smaller connectors with fewer pins. Skinny black flat connectors. Some are labeled, some aren't. Each goes to a specific component in the computer.
Here's a complete reference to every ATX power connector inside a modern desktop PC.
The big one: 24-pin ATX motherboard connector
The largest connector from your power supply, with 24 pins arranged in two rows. This is the main motherboard power connector that supplies +12V, +5V, +3.3V, and various control signals to the motherboard.
Older PCs (pre-2003) used a 20-pin version of this connector. The 24-pin standard added 4 extra pins to provide more power for newer hardware. Many 24-pin connectors are designed as "20+4" — the connector splits into a 20-pin section plus a removable 4-pin section, providing compatibility with older 20-pin motherboards.
The 24-pin connector is keyed (the housing has specific shapes that prevent reverse insertion) and locks into place with a small plastic tab. It's a tight fit and requires firm pressure to fully seat.
Critical: Always make sure all 24 pins are fully inserted. A partially seated 24-pin connector is one of the most common causes of "PC won't power on" issues. You should hear a clear click when the latch engages.
The 8-pin EPS / CPU power connector
A smaller 8-pin connector (sometimes split as 4+4) that supplies dedicated power to the CPU through the motherboard's CPU power circuitry.
The 8-pin EPS connector evolved from the older 4-pin ATX12V connector. As CPUs became more power-hungry, 4 pins weren't enough current capacity, so the spec doubled to 8.
You'll find this connector near the CPU socket on your motherboard — usually in the top-left corner. Some high-end motherboards have TWO 8-pin EPS connectors for extreme overclocking or workstation CPUs that draw significant power.
Don't confuse it with the 8-pin PCIe. They look similar (both are 8-pin) but the keying is different — they physically won't go into the wrong slot, but it's an easy mistake to grab the wrong cable.
PCIe power connectors (6-pin, 8-pin, 6+2-pin)
These power your graphics card directly. Modern GPUs draw far more power than the PCIe slot can provide (75W from the slot), so they have dedicated power connectors on the card.
6-pin PCIe connector — Provides up to 75W. Common on older or lower-end graphics cards.
8-pin PCIe connector — Provides up to 150W. Standard on most modern mid-range and high-end graphics cards.
6+2-pin PCIe connector — The 8-pin splits into a 6-pin section + 2-pin section, providing compatibility with both 6-pin and 8-pin graphics cards. Most modern PSU cables come in this configuration.
Cards may require 1, 2, or even 3 PCIe power connectors depending on power draw. A typical mid-range GPU uses one 8-pin connector. High-end cards (RTX 4070+, RX 7800 XT+) may use two 8-pins. Top-tier cards use three or the newer 12-pin/16-pin connector.
12VHPWR / 12V-2x6 (16-pin) — The newest PCIe power connector, introduced with the RTX 30/40 series. Provides up to 600W through a single connector. Some early implementations had melting issues with poorly seated connectors.
SATA power connectors
The flat black L-shaped connector with 15 pins. Used for connecting SATA hard drives, SSDs, and optical drives.
Most modern power supplies have one or more cables with multiple SATA power connectors daisy-chained (usually 3-5 per cable). The standard SATA power connector provides +12V, +5V, and +3.3V.
Some PSUs feature locking SATA power connectors with a metal clip that prevents accidental disconnection. Standard non-locking SATA power can work loose in cases that experience vibration.
Molex 4-pin (legacy peripheral)
The traditional 4-pin peripheral power connector with two large round pins (+12V and +5V) and two smaller rectangular pins (ground). Used since the 1980s for connecting hard drives and optical drives before SATA took over.
In modern PCs, Molex connectors are still used for:
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Case fans (especially older ones)
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Front-panel fan controllers
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RGB LED strips and controllers
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Some pump systems for water cooling
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Older PCIe expansion cards needing supplemental power
Molex connectors are durable but somewhat tedious to disconnect — they have no release latch, just friction. The trick is to wiggle slightly side-to-side while pulling, not to yank straight back.
Floppy drive connector (mini-Molex)
A smaller 4-pin connector once used for 3.5-inch floppy drives. Largely obsolete in 2026 but still present on some PSUs because:
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Some PCI sound cards use it for clean audio power
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Some industrial PCs still have floppy drives
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Some legacy equipment needs it
Don't confuse it with the larger standard Molex — the floppy connector is smaller with smaller pins.
Cable management features
Modern PSUs come in three configurations regarding cabling:
Non-modular — All cables are permanently attached to the PSU. Cheapest but messy because you can't remove unused cables.
Semi-modular — Essential cables (24-pin ATX, 8-pin CPU) are permanently attached. Optional cables (PCIe, SATA, Molex) connect via modular sockets on the PSU.
Fully modular — All cables connect via modular sockets. You only install the cables you actually need. Best for clean builds but slightly more expensive.
Important: Modular cables are NOT universally compatible between PSU brands or even between models from the same brand. Don't reuse modular cables from a different PSU — you can damage components from incorrect pinouts. Always use the cables that came with YOUR specific power supply.
Power supply wattage and cable count
A typical modern ATX PSU has:
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1× 24-pin ATX motherboard
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1× 8-pin EPS CPU (sometimes 2)
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2-4× 8-pin PCIe (more for higher wattage PSUs)
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6-10× SATA power
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2-4× Molex
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0-1× Floppy
Higher wattage PSUs (1000W+) have more cables to support multiple high-end GPUs or workstations with many drives.
Common build mistakes
Mistake 1: Not connecting the 8-pin CPU power. This is the second most common cause of PCs not powering on (after the 24-pin issue). The motherboard might appear to power on but won't POST without CPU power.
Mistake 2: Mixing modular cables between PSUs. Even if the cable fits, the pinouts may be different. Always use cables that match your specific PSU brand and model.
Mistake 3: Daisy-chaining too many high-power GPUs on a single cable. A single PCIe power cable from the PSU can supply two GPU connectors via daisy-chain, but high-end GPUs (like RTX 4080+) should each have their own dedicated cable from the PSU, not share one.
Mistake 4: Not fully seating the 12VHPWR connector. This is the connector that caused melting issues with early RTX 4090 cards. Make sure it's pushed in until the latch fully engages.
At Kentek, we carry power cables for PC builds including SATA power extensions, Molex-to-SATA adapters, and SATA power splitters.