Of the PCs that come in with "won't power on" or "reboots randomly", a huge fraction turn out to be PSU. And of those, several arrive with collateral damage — motherboard with bulged caps, dead SSD, GPU with permanent coil whine or outright fried. A bad PSU doesn't fail silently: it takes the rest with it.
What an ATX PSU actually does
It converts AC from the wall (110 V or 220 V) into stable DC at +12 V, +5 V and +3.3 V — the voltages components need. Sounds simple, but details matter:
- Regulation: voltages must stay within ±5% even when the GPU jumps from 30 W to 300 W in a millisecond (transient response).
- Ripple: the residual AC on DC voltages must be low (typically <50 mV on 12 V). High ripple degrades caps on board and GPU.
- Protections: must shut off before damage in a short, overvoltage, undervoltage or overcurrent. Cheap units often don't have these or have them miscalibrated.
- Efficiency: how much wall energy becomes component energy; the rest is heat.
80 Plus certifications, in plain English
80 Plus guarantees at least 80% efficiency at three load points (20%, 50%, 100%). Higher tiers are stricter:
| Level | Efficiency at 50% load | Real-world meaning |
|---|---|---|
| 80 Plus White | 80% | Minimum acceptable, nearly obsolete |
| 80 Plus Bronze | 85% | OK for budget builds |
| 80 Plus Silver | 88% | Rare on the market |
| 80 Plus Gold | 90% | Sweet spot for value |
| 80 Plus Platinum | 92% | Premium, less heat, longer life |
| 80 Plus Titanium | 94% | Top tier, justified in 24/7 servers |
The badge measures only efficiency, NOT regulation quality, NOT ripple, NOT protections, NOT cap quality. There are bad "80 Plus Gold" units and excellent "80 Plus Bronze" ones. To know real quality, check technical reviews on Cybenetics, HardwareLuxx, TechPowerUp, JonnyGuru / GamersNexus — they actually measure these.
Why a generic US$ 30 unit can kill your PC
A generic PSU says "750 W" on the box but actually:
- Lying label: that "750 W" might be a 1-second peak, not sustained. Real continuous capacity might be 400–500 W.
- No real protections: OCP (overcurrent), OVP (overvoltage), UVP (undervoltage), SCP (short), OTP (overtemp) — without these, any anomaly hits components.
- Cheap caps: generic Chinese caps dry up in 1–2 years and start delivering dirty voltage (high ripple), degrading everything else.
- Group Regulation design: saves cost but produces poor cross-regulation between rails (12V drops when 3.3V rises). Good units use DC-DC.
- Thin AWG cables: cables heat up, losses are high, connectors fail.
Summary: the "saved" PSU is a time bomb wired into the rest of the PC.
How to size the right wattage
Oversizing wastes money; undersizing causes damage. Reasonable rule:
- Calculate estimated peak draw of your components (GPU dominates). Use OuterVision PSU Calculator or Cooler Master's as a first cut.
- Add a 30–40% margin. PSUs are more efficient and last longer at 40–60% of nominal capacity, not at max.
- If your GPU is RTX 4070 Ti / 5070 or higher, consider ATX 3.0 / 3.1 PSUs with 12V-2x6 (12VHPWR) connector, designed to tolerate the transient spikes (up to 3× TDP).
| PC type | Recommended wattage |
|---|---|
| Office, no dedicated GPU | 350–450 W |
| Entry gaming (RTX 4060 / RX 7600) | 550–650 W |
| Mid gaming (RTX 4070 / RX 7700) | 650–750 W |
| High gaming (RTX 4080 / RX 7900 XT) | 850 W |
| Top tier (RTX 5090, Threadripper) | 1000–1200 W ATX 3.1 |
| Dual-GPU workstation | 1200–1600 W Platinum/Titanium |
How to spot a good PSU without being an engineer
- Known brand and model: Seasonic (Focus, PRIME), Corsair (RM/RMx/HXi), be quiet! (Pure Power, Straight Power), EVGA (G+, P+, SuperNOVA), MSI MEG/MPG, Cooler Master MWE Gold V2+, Asus ROG. Avoid budget-only "brand x" units.
- Check the OEM: many brands don't make their PSUs — Seasonic, CWT, Great Wall, FSP, Super Flower do. A "Corsair RMx" made by CWT is excellent; a "brand x" by unknown OEM, not.
- 10-year warranty is a signal: no maker gives 10 years on a bad PSU they'd be replacing three times.
- Recent technical review: search the exact model + "review" on Cybenetics or TechPowerUp. If absent or only in shopping sites without measurements, skip.
- Modular or semi-modular preferred: better cable management, less heat, more airflow.
How long does a good PSU last
A quality mid-range PSU properly sized in a well-ventilated PC typically lasts 8–12 years. Caps are what ages — sustained heat dries them out. That's why paying for Gold/Platinum with solid Japanese caps isn't vanity, it's 10-year savings.
A cheap generic lasts 1–3 years, and when it dies it doesn't die alone — it takes other components with high probability.
Protections you must verify
- OCP — shuts off if a line draws more amps than nominal.
- OVP / UVP — shuts off if voltages leave range.
- SCP — cuts immediately on a short.
- OPP — global total power protection.
- OTP — shuts off if internal temp passes threshold.
- Transient SIP / SCP — relevant for new GPUs with massive short spikes.
All must be in the manufacturer's spec sheet. If not, keep looking.
The most common mistake
People with US$ 2,000+ builds saving US$ 80 on the PSU. Any technician will tell you the same: the PSU is the last thing to swap and the first thing that destroys the rest. If budget is tight, cut from GPU or fancy case — never from the PSU.
Mid build: Corsair RM750e (ATX 3.0), Seasonic Focus GX-750 or be quiet! Pure Power 12 M 750W. High build with RTX 4080+: Seasonic Vertex GX-1000, Corsair RM1000x Shift or MSI MEG Ai1000P Platinum.
Building or upgrading a PC?
If you want a second opinion on your part list before buying, or want me to assemble it with parts that actually last, send me the list and I'll tell you what's fine and what I'd change. No purchase commitment.