The 6ES7405-0DA00-0AA0 is the PS 405 power supply module for the SIMATIC S7-400 rack. It takes a 24V DC input and delivers a regulated 5V DC backplane bus at 4A to power the CPU and I/O modules in the chassis.
No urgency to stockpile or search for surplus.
Integration into the S7-400 rack
The PS 405 snaps into the leftmost slot of the S7-400 rack and connects to the backplane via the module's own bus connector. No separate cabling to the backplane is needed — the module draws its input from the front-terminal 24V DC connection and feeds the 5V rail internally. Rated for 4A at 5V DC, this supply covers the backplane power budget for a typical mid-size S7-400 configuration with a CPU, a few I/O slices, and a communications processor. If the rack draws more than 4A on the 5V rail, step up to the 10A version (PS 407).