Why nameplate wattage is not enough
Most PSU calculators add up TDP figures and bolt on a fixed margin. That understates real draw in two specific ways, and both cause real failures.
Processors draw more than their rating. Intel's "processor base power" in particular is close to fiction under load — a chip rated at 125 W can sustain well over 200 W while gaming. We apply a per-architecture correction rather than trusting the sticker.
Graphics cards spike. Modern cards pull transient surges far above their board power rating for a few milliseconds at a time. Ampere and RDNA 2 cards are notorious for it. A supply sized to average draw can trip its own over-current protection and shut the machine down mid-game, even though every number on paper looked comfortable. That is why we size to peak, and why the recommendation is often higher than a simple sum would suggest.
Why we target around 60% load
Most supplies reach peak efficiency somewhere near half to two-thirds of their rating. Sizing there is not about saving electricity — the difference is pennies. It is about leaving genuine headroom for spikes, keeping the fan quieter, and being able to drop in a much faster graphics card in three years without buying a new supply.
Going much larger than that buys nothing. A 1200 W unit in a build drawing 300 W is not safer than a good 750 W unit; it is just more expensive and marginally less efficient at that load.
Quality matters more than wattage
The power supply is the one component whose failure can damage others. An 80 Plus rating certifies efficiency rather than build quality, but in practice the two correlate: manufacturers do not tend to put good internals behind a Bronze badge or bad ones behind Gold. A cheap 850 W unit is a worse buy than a good 650 W one for almost any build.
What you are really paying for is the quality of the components inside — capacitors that tolerate heat, protection circuits that trip before something is damaged, and a fan that does not fail in year three. None of that appears on the box, which is why brand reputation and independent teardown reviews matter more here than for any other part.
Cables, connectors and the 12V-2x6 question
Two practical points that cause more real failures than wattage does.
Do not daisy-chain PCIe cables on a high-draw card. Many supplies ship cables with two connectors on one run. On a card drawing 300 W or more, use separate cables from separate ports on the supply. Splitters are a common source of instability and of connectors running hotter than they should.
Seat the connector fully. The 12V-2x6 connector on recent high-end cards has a well-documented history of melting when partially inserted. Push until it clicks, check there is no gap at the shroud, and avoid a tight bend within about 35 mm of the plug. This is an installation problem rather than a design one, and it is entirely avoidable.
Use the cables that came with your supply. Modular cables are not standardised between manufacturers, and pinouts differ. A cable from a different unit can fit physically and deliver voltage to the wrong pins.
When to replace rather than reuse
A power supply is one of the few components genuinely worth carrying between builds, but not indefinitely.
- Age. Capacitors degrade. A unit past seven or eight years of regular use is worth replacing even if it still works, particularly if it was budget to begin with.
- A large jump in graphics card. Transient spikes have grown sharply across generations. An older supply sized adequately for its original card may trip its protection with a modern one even when average draw looks comfortable.
- Any symptom of instability. Random shutdowns under load, especially during scene transitions, are a classic sign of a supply that cannot handle spikes. They are often mistaken for a graphics driver problem.
Does a bigger supply cost more to run?
Barely, and probably not in the direction you expect. A supply draws what the system needs plus its conversion losses; it does not consume its rating. A 1000 W unit in a build drawing 300 W does not use 1000 W.
Efficiency does vary with load, peaking somewhere around half capacity on most units and falling off at very low load. The practical difference between a well-sized unit and an oversized one is a few percent of the power the system actually uses — pennies, not pounds. Size for headroom and quiet operation, not for an electricity bill.
If you are still choosing parts, the upgrade advisor will tell you whether a faster card is even worth it for your pairing before you size a supply around one.
Common questions
How many watts does my PC need?
Add the realistic draw of every component, then size the supply so it runs near 60% load. That keeps it in its efficiency sweet spot and leaves room for the brief current spikes modern graphics cards produce, which can trip a supply that was sized only to average draw.
Is a bigger power supply always better?
No. Beyond a comfortable margin, extra wattage buys nothing and costs more. A supply running at very low load is slightly less efficient than one near its sweet spot. Build quality matters far more than headline wattage.
Why does your recommendation exceed the manufacturer's?
It usually lands at or one retail step above NVIDIA's and AMD's published guidance, deliberately. Their figures assume a typical rest-of-system; ours accounts for what you actually selected, including processors that draw well above their rated base power.
Do these figures cover rendering and video work?
No — they are gaming figures. Sustained all-core work such as video rendering, 3D rendering or long compiles draws noticeably more from the processor. Add roughly 50% to the processor line if that is your main use.