A power supply unit (PSU) is an internal hardware component that converts alternating current (AC) from mains electricity into regulated low-voltage direct current (DC) required by computing equipment’s internal components including motherboard, CPU, GPU, and storage devices. In data centre contexts, power supply systems include redundant PSUs, uninterruptible power supplies (UPS), and power distribution units (PDUs) organised in hierarchical redundancy tiers.
Semantic Classification
Content
PSU Functions
Primary Functions
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AC to DC Conversion: Converts mains AC (110V/220V) to DC voltages (3.3V, 5V, 12V)
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Voltage Regulation: Maintains stable, consistent power delivery
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Power Distribution: Routes appropriate voltages to system components
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Protection: Overvoltage, overcurrent, and short-circuit protection
DC Output Rails
Rail Typical Use +12V CPU, GPU, drives, fans +5V USB ports, SATA drives, some components +3.3V RAM, chipsets, some peripherals -12V Legacy components +5VSB Standby power for wake functions Server and Data Center Power
Server PSU Characteristics
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Designed for 24/7 continuous operation
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Higher efficiency ratings (90%+ typical)
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Hot-swappable capability
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Redundant configurations
Redundancy Models
Configuration Description N+1 One spare PSU for failover 2N Fully redundant, two independent power paths 2N+1 Full redundancy plus one spare Data Center Power Hierarchy
- Utility Power: Main grid connection
- UPS Systems: Battery backup for immediate protection
- Generators: Extended backup during prolonged outages
- PDUs: Power distribution to racks and equipment
- Server PSUs: Final conversion for IT equipment
PSU vs PDU
| Aspect | PSU | PDU |
|---|---|---|
| Location | Inside computing device | In data center rack |
| Function | AC-DC conversion | Power distribution |
| Scope | Single device | Multiple devices |
| Features | Voltage regulation | Monitoring, switching, load balancing |
Efficiency Standards
80 PLUS Certification Levels
| Certification | Efficiency at 50% Load |
|---|---|
| 80 PLUS | 80% |
| Bronze | 85% |
| Silver | 88% |
| Gold | 90% |
| Platinum | 92% |
| Titanium | 94% |
Efficiency differences of 2% can significantly impact energy costs in large-scale data centers.