The power supply is the component people tend to skimp on, because it adds no performance and can't be seen. That's a mistake: a poor power supply can cause random reboots, instability that is hard to diagnose and, in the worst cases, damage other components when it fails. It's worth understanding what to look for.
What it does
The power supply converts the alternating current from the mains into direct current at different voltages: 12 volts for the processor, graphics card and motors, 5 and 3.3 volts for other circuits. It must do so with stable voltages even when the load changes abruptly, as happens when a graphics card goes from idle to full load in a few milliseconds.
It must also protect the system: a good power supply includes protection against overvoltage, undervoltage, overcurrent, short circuits and overheating, shutting down safely instead of passing the problem on to the components.
How much power you need
The correct way to estimate it is to add up the maximum draw of the main components and add a margin:
- the processor's maximum draw under load (which can exceed the stated TDP);
- the graphics card's draw, as given by the manufacturer;
- about 50-100 watts for motherboard, memory, drives, fans and USB devices;
- a 20-30% margin for spikes, ageing and future upgrades.
An example: a processor drawing 150 W under load, a 220 W graphics card and 75 W for the rest come to about 445 W. With the margin you get to around 550-650 W. A 1000 W unit wouldn't do any harm, but it would cost more without any real benefit.
Conversely, an office PC without a dedicated graphics card often draws less than 150 W even under load: a quality 400-450 W unit is more than enough.
80 Plus certifications
80 Plus certification indicates efficiency, i.e. how much of the energy drawn from the socket actually reaches the components and how much is lost as heat. The levels, in ascending order, are White (basic), Bronze, Silver, Gold, Platinum and Titanium.
Two important caveats:
- efficiency is not the same as overall quality: a Gold unit may have mediocre protection or stability, although more efficient models generally use better components;
- the difference on your electricity bill between Bronze and Gold, for a PC switched on a few hours a day, is modest; it becomes more interesting for computers that are always on or under load for many hours.
There are also other independent rating schemes that measure efficiency and noise with their own criteria; they can be useful for comparing similar models.
What matters beyond watts
- Capacitor quality and design: this determines stability and lifespan. Technical reviews that open the unit and measure voltages under load are the best source.
- Warranty: a long warranty, seven or ten years, is a good indicator of the manufacturer's confidence in the product.
- Modular cables: they let you connect only the cables you need, improving tidiness and airflow. Always use the original cables of the same unit: the pinout on the power-supply side is not standard, and cables from another model can destroy components.
- Noise: many units stop the fan at low load, making the PC silent during light use.
ATX 3.0 and the graphics card connector
The latest high-end graphics cards can have very short but very high power spikes. Power supplies compliant with ATX 3.0 and later specifications are designed to tolerate these spikes and often include the 16-pin connector (12VHPWR or its 12V-2x6 revision) for these cards.
With this connector there is one rule: push it all the way in, without bending the cable sharply near the plug. Partial contact can cause the connector to overheat.
Signs of a struggling power supply
- sudden reboots or shutdowns under load, for example when a game starts;
- the PC won't turn on but the motherboard shows standby lights;
- humming, electrical whining or a burning smell;
- a noisy or stuck fan.
In my work, when faced with instability that can't be explained by software or temperatures, the power supply is one of the first suspects: trying a unit that is known to work quickly settles the question.
Safety
The power supply contains capacitors that can stay charged even after being unplugged. It must never be opened: if it's faulty, replace it. Switch off at the rear and remove the cable before working inside the case.
In short
- Work out the wattage by adding real power draws and a 20-30% margin.
- 80 Plus measures efficiency, not overall quality.
- Protection, components and warranty matter more than the stated wattage.
- Use only the original modular cables and seat high-power connectors fully.
- A faulty power supply is not opened: it is replaced.
