PDF schematic, 1.15 MB, labelled PS-5161-1D1S, a code that looks like a power-supply unit model number. The name says nothing more about the device, wattage or revision, so compare the code against the label on the actual PSU before relying on it. A power-supply diagram helps a technician follow the primary side from the mains filter and bridge rectifier to the switching stage, check the feedback loop and standby circuit, and identify the secondary rectifiers. Discharge the primary capacitors before probing a unit that has been connected to the mains.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @BoardSchematic. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.