Finding the best 1000W power supplies under £100 used to mean making real compromises. Dodgy capacitors, noisy fans, efficiency ratings that barely scraped Gold. Not anymore. The budget PSU market has genuinely improved, and right now you can get a fully modular, ATX 3.1-compliant, 80 Plus Gold unit for well under a hundred quid. We've pulled together four of the strongest options available in the UK right now and ranked them honestly, including a couple of genuine surprises. Whether you're building a high-end gaming rig around an RTX 4080 or just want proper headroom for future upgrades, there's something here for you.
Buying Guide: What to Look For in the Best 1000W Power Supplies Under £100
Buying a PSU is one of those decisions that's easy to rush. You pick a wattage, check the price, and move on. But the PSU is the one component that every other part in your system depends on. Get it wrong and you're looking at instability, crashes, or in the worst case, damage to expensive hardware. Here's what actually matters.
Efficiency Ratings: Gold, Platinum, and Cybenetics
80 Plus Gold is the baseline you should accept at this price point. It means the unit is at least 87% efficient at 20% load, 90% at 50%, and 87% at 100%. That leftover percentage becomes heat, so higher efficiency means a cooler, quieter PSU. Cybenetics is a separate certification body that many consider more rigorous. If a unit carries both 80 Plus Gold and Cybenetics Platinum, that's a strong signal of genuine quality. Two of the four units in this roundup carry both.
ATX 3.1 and PCIe 5.1: Do You Need Them?
If you're buying a new GPU from the RTX 40 series or RX 7000 series, yes. ATX 3.1 improves how the PSU handles sudden power spikes (called transient loads), which modern GPUs produce more aggressively than older cards. PCIe 5.1 with the 12V-2x6 connector is the safer, more reliable version of the 16-pin connector that caused some melting issues on early RTX 4090 builds. All four PSUs here support this, which is good to see across the board.
Modular vs Semi-Modular vs Non-Modular
At this price point, all four options are fully modular. That's the right choice. You only connect the cables you need, which makes cable management cleaner and improves airflow. Semi-modular units have fixed ATX and CPU cables, which is a minor inconvenience. Non-modular units are a cable management nightmare and have no place in a build at this budget.
Capacitor Quality
Look for 105°C-rated Japanese capacitors. The temperature rating tells you how much heat stress the caps can handle before degrading. 85°C caps are cheaper and more common in budget units. 105°C caps last longer, particularly in warmer environments. The ENDORFY Supremo FM6 explicitly lists 105°C caps, which is worth noting.
Warranty Length
A five-year warranty is the minimum you should accept. Seven years is good. Ten years is exceptional, and the Montech Century II is the only unit in this roundup offering that. A longer warranty isn't just peace of mind. It's a signal that the manufacturer is confident in the build quality.
Wattage: How Much Do You Actually Need?
For a system with an RTX 4080 and a modern Intel or AMD CPU, 850W is usually sufficient. 1000W gives you comfortable headroom for overclocking, additional storage, and future upgrades. Going above 1000W (like the Montech Century II at 1200W) only makes sense if you're planning an extreme build or want maximum future-proofing. Running a PSU at 50% to 70% of its rated capacity is the sweet spot for efficiency and longevity.
How We Selected These Best 1000W Power Supplies Under £100
We shortlisted units based on current UK availability, verified Amazon pricing under the £100 threshold, and cross-referenced specifications against manufacturer documentation. We assessed efficiency certifications, connector compatibility with current GPU generations, capacitor quality, warranty terms, and real-world owner feedback from verified UK buyers. We also consulted independent PSU testing data from established tech review outlets to validate manufacturer efficiency claims. Units with known reliability issues or unverified specifications were excluded from consideration. The goal was a shortlist of four units that a real person could buy today with confidence.
