This accessory can be used to operate the System One 60 Series when AC power is not available. The power outlet adapter end of the Shielded DC Cord can plug into a standard 12 volt power outlet found in cars, the socket on the Respironics Battery Pack, or to the terminals of a separate external battery. Please Note: This cord works ONLY with PR System One 60 Series machines and is not compatible with any other machines made by Philips Respironics or other manufacturersNot sure if you have the 50 or 60 Series Machine ?Machine Color: The color of your machine is one way to verify your machine series type. The 60 Series machines are charcoal gray with metallic silver side and instrument panels. The 50 Series machines are dark gray with ivory colored side and instrument panels.Machine Branding: There is a slight branding difference between the 50 and 60 Series. The 60 Series machines have the words System One in raised or letters stamped in silver on both the machine and humidifier. The 50 Series machines do not have raised lettering and the branding information is painted onto the unit. Machine Reference Number: The reference number of both Series is located on the bottom of the unit. A device type with REF of 560P printed on the bottom indicates a 60 Series while 550P would indicate a 50 Series. Another example would be the 460P (60 series) and the 450P (50 Series).This 12 Volt DC Cord is compatible with the following Machines: All Philips Respironics 60 Series PR System One CPAP and Bipap MachinesDS220S and DS220HS DS260S and DS260TS DS460S and DS460TS DS560S and DS560TS DS660S and DS660TS DS760S and DS760TS This cord CANNOT be used with PR System One 50 Series Machines. If you need the DC Cord for the 50 Series: Click Here.