How to Choose a Power Supply (PSU) for Your PC

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Ankit Kumar
Buying GuideHardwareUpgrade

The Problem

The power supply is the one part of a PC that can take every other part with it when it fails. It is also the part people most often cheap out on, because it does not add any frames per second.

Picking a good one is simpler than the spec sheets make it look. You need the right wattage, the right connectors for your graphics card, a sensible efficiency rating, and a unit from a reputable model line.

Step 1: Work Out the Wattage

Add up the two big consumers, then add headroom.

  1. Graphics card: use the total board power (TBP or TGP) from the manufacturer's spec page.
  2. CPU: use the maximum power draw, not the TDP on the box. Mainstream CPUs typically draw 65–150 W under load, high-end desktop chips 200–250 W.
  3. Add about 100 W for the motherboard, RAM, drives, fans, and USB devices.
  4. Multiply by about 1.4 for headroom.

Example: a 220 W GPU + 125 W CPU + 100 W = 445 W. × 1.4 ≈ 620 W, so a good 650 W unit.

The GPU manufacturer's recommended PSU figure is a safe shortcut — it already includes headroom for a typical high-end CPU.

Why Headroom Matters

Modern graphics cards produce transient spikes — bursts lasting milliseconds that can exceed the rated power by a large margin. A PSU running close to its limit can shut down under these spikes, which looks like a random restart during games. Headroom also keeps the PSU in its most efficient and quietest range, around 40–60% load.

Buying far more than you need (1200 W for a 400 W system) is wasted money, but it does no harm.

Step 2: Check the GPU Connector

  • Most graphics cards use 8-pin PCIe (sometimes called 6+2-pin) connectors. Count how many your card needs and make sure the PSU has that many separate cables.
  • High-end NVIDIA cards (and some others) use the 12V-2x6 connector, a revised version of 12VHPWR. A PSU built to ATX 3.1 includes a native 12V-2x6 cable, which is neater and more reliable than an adapter.

For a 12V-2x6 cable, push it in until it clicks and sits completely flush, and avoid sharp bends close to the plug. A partly inserted connector is the main cause of the melted-connector reports.

If a card needs two or three 8-pin connectors, use separate cables from the PSU for each, rather than a single cable with two plugs on it (a "daisy chain"), for higher-power cards.

Step 3: Understand Efficiency Ratings

80 Plus ratings describe how much of the power drawn from the wall reaches your components.

| Rating | Efficiency at 50% load (115 V) | |---|---| | 80 Plus Bronze | ~85% | | 80 Plus Gold | ~90% | | 80 Plus Platinum | ~92% | | 80 Plus Titanium | ~94% |

Gold is the sweet spot for most builds. The electricity savings between Bronze and Gold are small, but Gold units are usually built with better components overall.

The efficiency rating is not a quality rating. A well-built Bronze unit is better than a poorly built Gold one. Cybenetics ratings (ETA for efficiency, LAMBDA for noise) test more thoroughly than 80 Plus and are worth checking where available.

Step 4: Choose the Form Factor and Cabling

  • ATX fits most desktop cases. SFX and SFX-L are for small form factor cases — check your case's specifications.
  • Fully modular PSUs let you attach only the cables you need, which makes building and airflow easier. Semi-modular has the main motherboard and CPU cables fixed. Non-modular is cheapest and fine in a case with good cable space.
  • Check the PSU length against your case's maximum. Higher-wattage ATX units are often longer.

Step 5: Judge Quality

Brand names alone are not reliable — most brands sell both excellent and poor model lines, built by different factories.

  • Look up independent reviews of the exact model, from reviewers that load-test PSUs with proper equipment.
  • Warranty length is a good signal. Good units carry 7–12 years; budget units often 2–3.
  • Look for the full set of protections: OCP, OVP, UVP, SCP, OPP, and OTP (over-current, over-voltage, under-voltage, short-circuit, over-power, over-temperature).
  • Avoid unbranded units bundled free with cases, and any unit whose wattage claim looks too good for the price.

Mistakes That Damage Hardware

  • Never reuse modular cables from a different PSU, even from the same brand. The pin layout at the PSU end is not standardised, and the wrong cable can send 12 V down a 5 V or 3.3 V line and destroy drives, the motherboard, or the GPU.
  • Don't use SATA or Molex-to-PCIe adapters to power a graphics card. They are not rated for the current.
  • Don't open a PSU. The capacitors inside can hold a dangerous charge long after the unit is unplugged.

When to Replace an Existing PSU

  • You are upgrading to a graphics card that exceeds the current PSU's wattage or needs connectors it does not have.
  • The PC restarts or shuts off under gaming load, especially after a GPU upgrade.
  • The PSU is more than 7–10 years old or past its warranty, particularly before an expensive upgrade.
  • You hear coil whine or clicking from the PSU, or smell burning.

For the rest of the upgrade path, see best PC upgrades to speed up an old computer. If the PC does not power on at all, start with fix a PC that won't turn on.

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