#cs#hardware#psu#power
Power Supply (PSU) and 80 Plus Ratings
If your computer keeps randomly rebooting, it might be a cheap PSU. A steady heartbeat keeps the body (and computer) alive.
February 16, 2025
Codemapo
If your computer keeps randomly rebooting, it might be a cheap PSU. A steady heartbeat keeps the body (and computer) alive.
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My PC used to shut down randomly during gaming sessions. Virus? Bad RAM? Dying GPU? I tried every troubleshooting step, but only found the real culprit at the repair shop. "Your power supply is fried. That's what happens with cheap no-name PSUs."
Power Supply Unit (PSU). I thought it was just a plug socket for the power cord. Turns out, it's the heart of the computer. And when the heart has arrhythmia (unstable voltage), the brain (CPU) and muscles (GPU) all shut down.
That day changed how I build PCs. I learned that a stable heart matters more than an expensive CPU or flashy RGB coolers.
When I first heard about PSU's role, I didn't get it. "Converts AC to DC" meant nothing to me. I knew what AC and DC were, but why convert? How does it work?
Then I heard this analogy and everything clicked. "A PSU is like a water purification plant."
Electricity from the wall outlet is 220V AC (Alternating Current). The voltage swings between positive and negative, back and forth. It undulates like ocean waves. Think of it as river or ocean water. It flows, but it's full of impurities and the pressure fluctuates.
Computer components need 12V, 5V, 3.3V DC (Direct Current). Voltage flows in one direction and maintains a steady level. Like calm lake water. They need purified, clean water with consistent pressure and no contaminants.
The PSU takes rough waves (AC 220V) and transforms them into calm water (DC 12V). It's a purification plant and conversion system rolled into one.
Inside the PSU, this is what happens:
Cheap PSUs have terrible purification processes. Noise (impurities, ripples) gets mixed into the DC power. For sensitive semiconductor components, this is poison. That's why computers suffer shock death (reboot, shutdown).
Voltage fluctuation is called ripple. Good PSUs keep ripple under 50mV. Almost no waves. Cheap PSUs have ripple exceeding 200mV. Choppy waters.
My random shutdown during gaming was caused by ripple. When the GPU draws massive power, if the PSU can't stabilize voltage, you get momentary voltage drop to the CPU or memory. The system just stops. Protection circuits kick in and shut everything down.
After understanding this, I really got why the PSU is the heart. When your heart beats irregularly (arrhythmia), oxygen supply to the brain becomes unstable, and you collapse. When the PSU delivers unstable voltage, power supply to the CPU fluctuates, and the computer crashes.
When buying a PSU, you see "80 Plus Standard, Bronze, Gold" ratings. At first I thought "Gold is better because it's gold", but it's actually about efficiency.
I didn't understand efficiency until I saw this calculation.
This means the PSU itself becomes a heating device. 125W is like running two incandescent light bulbs continuously. Inside your case, you're running two light bulbs 24/7.
Low efficiency creates two problems:
After switching to a Gold-rated PSU, I noticed reduced fan noise. My old PSU's fan roared under load. The Gold-rated one stayed quiet. Less heat means the fan doesn't need to spin hard.
| Grade | 50% Load Efficiency | 100% Load Efficiency | Notes |
|---|---|---|---|
| 80 Plus | 80% | 80% | Minimum standard |
| Bronze | 85% | 82% | Budget tier |
| Silver | 88% | 85% | - |
| Gold | 90% | 87% | Best value sweet spot |
| Platinum | 92% | 89% | High-end |
| Titanium | 94% | 90% | Datacenter grade |
Interesting fact: efficiency varies with load. Most PSUs hit peak efficiency at 50% load. That's why you should get a PSU with 2x your maximum power consumption.
For example, if my system peaks at 400W, I use a 750W-850W PSU. That way it runs at 50% load for optimal efficiency during normal use.
The 'fake PSU' I got burned by claimed 500W but couldn't sustain even 200W. What this really means is they lied about the 12V rail capacity.
PSUs output multiple voltages:
Modern systems draw most power from the 12V rail. CPU and GPU pull power from here.
The fake PSU trick goes like this:
So CPU and GPU only get 200W to share. Modern high-end graphics cards alone consume 300W. No wonder the PC crashes during gaming.
Good PSUs deliver 90%+ of total capacity on the 12V rail. For example, a Seasonic 650W PSU can deliver 648W on 12V alone.
When building my AI training server with an RTX 4090, I learned this the hard way. That GPU has 450W TDP. Add CPU at 125W and other components at 75W, that's 650W total.
But transient power spikes can reach 1.5x TDP. The GPU can momentarily pull 675W.
That's why I went with a 1000W Gold-rated PSU. Normal operation runs at 60-70% load for peak efficiency, and it handles spikes with headroom.
Another confusing choice was Modular vs Non-Modular PSUs.
At first I thought "How bad can cable clutter be?" After using both, I noticed a real airflow difference. Non-modular PSUs have bundles of unused cables blocking air circulation. Fully modular keeps the case clean, and air flows smoothly.
For servers, I always go fully modular. Maintenance is way easier when you can detach cables individually.
12V rails come in Single-Rail and Multi-Rail configurations.
I initially thought "Multi must be better, right?" But modern trend favors single-rail.
Why? High-performance GPUs need to draw massive bursts of power instantly. Multi-rail has current limits per rail, causing OCP false triggers.
Single-rail lets you freely use the entire 12V capacity, ideal for high-performance builds. The PSU still has overall OCP for safety.
The biggest question when choosing a PSU: "What wattage do I need?"
I initially thought "Just add up component TDPs." That's not quite right.
Sites like https://outervision.com/power-supply-calculator give accurate calculations.
Input:
You get a recommended PSU wattage.
Example for my main PC:
→ Result: Recommended 850W, safely 1000W
I went with 1000W Gold to leave upgrade headroom. If I upgrade to RTX 5090 later, same PSU works.
If you plan to overclock, add +20% headroom. Overclocked CPUs can jump from 200W to 300W.
Setting up company servers, I first encountered redundant PSUs. Server chassis hold two PSUs.
For cloud services, one server crash means revenue loss. Mission-critical servers always use redundant PSUs.
Cost is 2-3x regular PSUs, but it's insurance for zero downtime.
Linux server commands for PSU monitoring:
# Check total power consumption (requires ipmitool)
sudo ipmitool sensor | grep -i power
# Sample output:
# PSU1_Input | 425 Watts | ok
# PSU2_Input | 430 Watts | ok
# Total_Power | 855 Watts | ok
# Check CPU/GPU temperature and power
sensors
# Monitor GPU power with nvidia-smi
nvidia-smi --query-gpu=power.draw,power.limit --format=csv --loop=1
I run these monitors on all servers and visualize in Grafana. Alerts trigger when power usage exceeds 90% of rated capacity.
Even the best PSU is useless during a power outage. Servers need UPS (Uninterruptible Power Supply).
UPS setup example (Linux):
# Install NUT (Network UPS Tools)
sudo apt install nut
# UPS config: /etc/nut/ups.conf
[myups]
driver = usbhid-ups
port = auto
desc = "Server UPS"
# Auto-shutdown config: /etc/nut/upsmon.conf
MONITOR myups@localhost 1 admin password master
SHUTDOWNCMD "/sbin/shutdown -h +1"
# Safe shutdown when battery hits 20%
Home PCs can plug into power strips, but servers need UPS. During outages, you get 5-10 minutes to save work and shut down safely.
| Grade (80 Plus) | Efficiency (at 50% Load) | Recommended For |
|---|---|---|
| Standard | 80%+ | Office, Low-end PC |
| Bronze / Silver | 85%+ | Budget Gaming PC |
| Gold | 90%+ | High-end, 24/7 Servers |
| Platinum / Titanium | 92~94%+ | Workstation, Datacenter |
When a CPU or RAM dies, they die alone. But when a PSU explodes, it drags the motherboard and GPU to hell.
Here's what I've learned about PSUs:
That's why experts choose the PSU first when building. For servers, I always use Gold-rated or higher from reputable brands (Seasonic, FSP, Corsair). Stability is something you pay for.