Computers, Laptops & Tablets > Accessories & Hardware 136 136 people found this article helpful Power Supply Voltage Tolerances Proper voltage ranges for ATX power supply voltage rails By Tim Fisher Tim Fisher Facebook Twitter Senior Vice President & Group General Manager, Tech & Sustainability Emporia State University Tim Fisher has more than 30 years' of professional technology experience. He's been writing about tech for more than two decades and serves as the VP and General Manager of Lifewire. lifewire's editorial guidelines Updated on August 19, 2021 Tweet Share Email Accessories & Hardware The Quick Guide to Webcams Keyboards & Mice Monitors Cards HDD & SSD Printers & Scanners Raspberry Pi The power supply in a PC supplies various voltages to internal devices in a computer through power connectors. These voltages don't have to be exact, but they can only vary up or down by a certain amount, called a tolerance. If a power supply is providing the parts of a computer with a particular voltage outside this tolerance, the devices being powered may not work properly—or at all. Below is a table listing the tolerances for each power supply voltage rail according to Version 2.2 of the ATX Specification (PDF). Thermaltake Dr. Power II Automated Power Supply Tester. Thermaltake Power Supply Voltage Tolerances (ATX v2.2) PSU Tolerance Table Voltage Rail Tolerance Minimum Voltage Maximum Voltage +3.3VDC ± 5% +3.135 VDC +3.465 VDC +5VDC ± 5% +4.750 VDC +5.250 VDC +5VSB ± 5% +4.750 VDC +5.250 VDC -5VDC (if used) ± 10% -4.500 VDC -5.500 VDC +12VDC ± 5% +11.400 VDC +12.600 VDC -12VDC ± 10% -10.800 VDC - 13.200 VDC To help when testing a power supply, we've also calculated the minimum and maximum voltages using the tolerances listed. You can reference our ATX Power Supply Pinout Tables list for details on which power connector pins supply which voltage. Power Good Delay Power Good Delay is the amount of time it takes a power supply to start up completely and begin delivering the proper voltages to the connected devices. According to the Desktop Platform Form Factors Power Supply Guide [PDF], Power Good Delay, referred to as PWR_OK delay in the linked document, should be 100 ms to 500 ms. Was this page helpful? Thanks for letting us know! Get the Latest Tech News Delivered Every Day Email Address Sign up There was an error. Please try again. You're in! Thanks for signing up. There was an error. Please try again. Thank you for signing up! Tell us why! Other Not enough details Hard to understand Submit More from Lifewire How to Manually Test a Power Supply With a Multimeter What Is a Power Supply Voltage Switch? How to Use a Power Supply Tester to Test a PSU ATX Power Supply Pinout Tables Molex 4-pin Peripheral Power Connector Pinout Computer Power Supply SATA 15-Pin Power Connector Pinout How to Size an Uninterruptible Power Supply How to Install a Desktop Power Supply The 9 Best Uninterruptible Power Supplies (UPS) of 2022 How to Fix a Computer That Turns on but Displays Nothing ATX 24-pin 12V Power Supply Pinout Computer Power Supply Wattage How to Upgrade a Graphics Card What Are the Types of Uninterruptible Power Supplies? How Do I Test the Power Supply in My Computer?