Quick answer: If a PC has no power, intermittent startup, or shutdown under load, check only the external power path and record when the fault occurs. Stop for burning odor, smoke, unusual heat, liquid, or damaged wiring. Never open or test inside the PSU.
Before you start
- Tools: the product manual, good lighting, a soft dry cloth, and one known-good compatible cable or accessory if relevant
- Time: 15–45 minutes for external checks
- Difficulty: Pro only
- Safety: Never open a PSU. Capacitors can retain dangerous voltage after unplugging. Mains-side diagnosis and internal repair are professional-only.
Back up accessible data before updates. Work on a stable, dry surface and disconnect power before moving cables or removable hardware.
Causes ranked by likelihood
| Cause | How to check | Fix | Difficulty |
|---|---|---|---|
| 1. No power or intermittent startup | Check external outlet, cable, and case indicator | Replace only a damaged external lead with an approved one | Easy |
| 2. Shutdown under load | Note when the shutdown occurs; check exterior vents | Stop repeated loading and seek qualified diagnosis | Pro |
| 3. Electrical odor, noise, or overheating | Observe symptoms without opening enclosure | Disconnect power; do not open or test PSU internals | Pro |
| 4. Another component mimicking PSU failure | Record external symptoms and POST indicators | Have a technician isolate the fault | Pro |
Key takeaway: 1. No power or intermittent startup: how to check — Check external outlet, cable, and case indicator.
1. Check no power or intermittent startup
Check the external power cable, outlet, and case power indicator without opening the PSU. Disconnect power if there is odor, smoke, sparking, or unusual heat; do not attempt internal PSU testing.
2. Isolate shutdown under load
Record whether shutdown occurs only under heavy load and check for blocked exterior vents. Repeated shutdown, electrical odor, or unusual heat calls for qualified diagnosis; never open a PSU.
3. Evaluate electrical odor, noise, or overheating
If the PSU area emits a burning odor, crackling, smoke, or unusual heat, switch off and disconnect the PC. Do not open the PSU, run repeated start attempts, or use an improvised jumper test.
4. Treat another component mimicking psu failure as an escalation point
No-power symptoms can also originate from a switch, motherboard, or outlet. Record the external signs and ask a qualified technician to distinguish them rather than declaring the PSU defective from one symptom.
Brand-specific notes
PSU cables and pinouts are not universally interchangeable. Use only cables explicitly approved for the exact PSU model; never open the enclosure.
When to call a professional
Arrange qualified service for a burning smell, smoke, arcing, liquid inside, damaged mains connector, swollen battery, repeated protection shutdown, precision alignment, soldered port, or a fault that requires energized measurements. For valuable data on a failing drive or card, stop writing to it and consult a recovery specialist.
Prevention tips
- Keep the PC's external vents clear using the maker's approved method; do not open the PSU to clean it.
- Avoid strain or damage to the mains lead and use only compatible PSU cables.
- Maintain backups before faults occur; do not rely on repeated starts to diagnose a failing supply.
Related help
- Back to Power Supply (PSU) Guide
- PSU Wattage Calculator Guide: Size It Correctly
- Electronics safety basics
Official resources
Summary
Begin with the most likely external cause, verify the complete power or signal path, and test one known-good compatible item at a time. Model-specific documentation outranks generic reset advice. Stop before a low-risk check becomes internal powered work, battery damage, precision mechanical damage, or data loss.
Observations that narrow down psu failure signs and safe next steps
| What you observe | What it may indicate | Safe next step |
|---|---|---|
| Computer has no power but outlet works | Power path may be at fault | Check only external cable and switch status; avoid opening the PSU. |
| System shuts down under load | A PSU issue is possible but not proven | Record workload and symptoms for a qualified technician. |
| Electrical odor or arcing is present | Immediate safety hazard | Stop use and have the supply professionally replaced or assessed. |
Key takeaway: Computer has no power but outlet works: what it may indicate — Power path may be at fault.
Key takeaway: For psu failure signs and safe next steps, compare the observation with one safe, reversible check before assuming a part has failed.