SFX/SFX12V Power Supply Specifications

Although it is derived from the ATX/ATX12V and NLX specifications, SFX/SFX12V makes compromises to permit lower-cost power supplies that meet the needs of inexpensive systems. SFX systems are designed to be low-cost, and the SFX specification reflects this with less-stringent requirements than the ATX and NLX specifications.

First-generation SFX 1.1 power supplies were designed to provide 90W maximum continuous power, with peak power of 135W for 15-second durations on a 5-minute duty cycle. Current SFX 2.1 power supplies provide higher currents to support the Pentium 4 and other power-hungry processors. The SFX Power Supply Design Guide Version 2.1 defines the SFX voltage rails and tolerances shown in Table 26-6. An SFX 2.1-compliant power supply must provide these voltages with these tolerances or better.

Table 26-6. SFX/SFX12V power supply voltage rails and tolerances

Voltage rail

























+12VDC (peak load)










The SFX Power Supply Design Guide Version 1.1 defined only one wattage for an SFX power supply. The SFX Power Supply Design Guide Version 2.1 defines three SFX configurations, shown in Table 26-7.

Table 26-7. Typical power distribution for SFX power supplies


120W SFX

150W SFX

Voltage ...

Get PC Hardware in a Nutshell, 3rd Edition now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.