I'm confused about this component that distributes power to computer hardware. How does it stabilize the voltage coming directly from the electricity? What kind of protections does it have, especially against current fluctuations? And what about these things called 'redundant power supplies'—how should one choose between them?
What is a PSU and how does it work?
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The main job of a PSU (Power Supply Unit) is to convert the irregular AC power coming from the wall into the appropriate DC voltage and stable current for your system's components. For example, in a 750W model, after capturing the primary circuit voltage, it adjusts the output to voltages like 12V, 5V, and 3.3V through a chain of main transformer, rectifier (diode), and filters (capacitors). The critical role here is played by the switching frequency and PWM (Pulse Width Modulation) controls: when there are sudden load changes (CPU/GPU spikes), the VRM modules kick in and protect sensitive components.
As for surges or sudden voltage drops, I've experienced that the protection circuits work simply. A good PSU has systems like OVP (Over Voltage Protection), UVP (Under Voltage), OCP (Over Current), SCP (Short Circuit), and even OTP (overheating). For instance, in my 850W Seasonic Focus GX-850, there's a slight delay in fan spin-up with the "DC OK" signal, thus protecting the system against temperature fluctuations.
Redundant power supplies, on the other hand, are ideal for server-style environments or systems that run continuously. For example, if you run two 500W units in parallel and the system draws 1000W, if one fails, the other kicks in without dropping the load below zero. Things to consider when choosing one include: same model/wattage values, hardware that supports parallel operation, and most importantly, equal fan noise for stable load distribution.
The PSU stabilizes voltage using internal "transformers" and "converter circuits" to step down the voltage and smooth it out with capacitors. It has "thermal protection" and "overvoltage protection (OVP)" circuits to guard against current fluctuations, shutting down automatically at the slightest sign of trouble. If you're looking for a backup power supply that keeps running even during blackouts, you'll want a UPS (uninterruptible power supply)—but that’s a whole other story.