To tell PSU without opening the case, the most reliable method is to photograph the power supply label through your computer's rear vents using a flashlight and smartphone camera. This approach lets you read the brand, model number, and total wattage directly from the label without removing any panels.
Check your purchase history or receipts
Reviewing your original purchase documentation is the fastest way to identify a PSU for a custom-built PC. Check your Amazon, Newegg, or other online retailer order history for the exact item purchased. The invoice or order details should list the PSU's model number and wattage, which you can verify against the component's product page. This method works even if the PSU is no longer installed in the original system, as long as you haven't upgraded it since the purchase.
Look up your pre-built PC's serial number
Navigate to the official website, locate the "Support" section, and enter your PC's model name or serial number. The product specifications page or downloadable manual will list the original PSU details, including its form factor and wattage capacity. This method is most effective when the PSU has not been replaced since the original purchase.
Read the PSU label through the case vents
Locate the PSU label on the back of your computer where the power cord connects, or on the side of the power supply facing the interior. Use a flashlight to illuminate the area and a smartphone camera to take a high-quality photo through the case vents or mesh shroud. Zoom in on the photo to read the brand name, model number, total wattage (listed as "Max Output" or "Total Power"), and any 80 Plus certification logo. This non-invasive method works for most desktop cases with visible ventilation.
Check the PC exterior and UL label
Examine the exterior of your computer for labels or stickers that may contain power supply specifications, including its make, model, and maximum power output. If the PSU information is unclear, locate the Underwriters Laboratories (UL) label near where the power cord connects to the case. Go to the UL website and type in the UL serial number to search for information in their database, which can reveal the PSU's manufacturer and specifications.
Consult the original manual or documentation
Find the PC's or PSU's manual or documentation that came with the product. Look for a section titled "System Configuration" or "Power Supply." Check for specifications such as maximum power output, voltage information, and other technical specifications. This method works for both pre-built systems and aftermarket PSUs if you still have the original paperwork.
Use software and hardware tools for estimation only
Software tools like HWMonitor, Open Hardware Monitor, or HWiNFO64 can display real-time voltage readings (+12V, +5V, +3.3V) and estimate the power draw of components like the CPU and GPU. These monitoring tools are useful for assessing if the PSU is currently providing stable power and meeting component demands, but they do not reveal the PSU's maximum rated capacity. PSUs do not communicate their specific model or wattage information to the operating system, meaning no software can accurately query this data. A Kill-A-Watt meter can measure the real-time total power consumption of the entire system from the wall outlet during a stress test, indicating actual power draw, but not the PSU's rated wattage. If you suspect instability under load, you can also check if GPU is getting enough power by watching for voltage drops in these readings. Online PSU calculators can estimate the minimum wattage required for a system based on its components, which can help infer if an existing PSU is sufficient if the system is stable, but they do not identify the installed PSU.
When you may need to open the case after all
If all non-invasive methods fail, physically inspecting the label on the PSU itself is the only authoritative source for its model and wattage specifications. The physical label located on the PSU is considered the only authoritative source for its model and wattage specifications. Opening the case requires powering off and unplugging the computer, then removing the side panel to access the PSU label directly. For laptops, the power supply information, including wattage, is typically found on the external brick adapter rather than inside the device.
