What the 600W rating means for your board
The P6KE400A-T: The 548V clamping voltage at 1.1A peak pulse current means a transient that would otherwise punch through a 342V DC rail gets folded back to a level the downstream silicon can survive.
DO-15 axial footprint and integration
Housed in a DO-204AC (DO-15) axial-lead package, the part mounts through-hole — the leads are formed to drop into a 0.7 mm diameter plated hole on a standard 0.4-inch lead spacing. The through-hole body handles the thermal pulse of a 600W surge better than a comparable SMD package because the lead frame and the copper pad on the PCB sink heat directly into the board's copper pour.
Lifecycle reality — obsolete, sourced to order
Diodes Incorporated lists the P6KE400A-T as Obsolete. No pin-compatible direct replacement is documented; a functional equivalent would need to match the 342V standoff, 548V clamp, and 600W peak pulse rating in a DO-15 package.