What the 1.5kW rating means for your rail
The 1.5KE400-E3/73: That 574V clamping voltage at 2.6A peak pulse current tells you the rail it protects must tolerate that transient ceiling without secondary breakdown. With a 324V reverse standoff voltage and a minimum breakdown of 360V, this part sits on a nominal 300V DC bus or a 240V AC rectified line — the standoff is the continuous DC bias the diode ignores, and the breakdown is where it starts conducting. The 175°C max junction temperature gives headroom in a sealed enclosure.
Obsolete — what that means for procurement
Vishay lists the 1.5KE400-/73 as obsolete. The DO-201AA axial-lead package is a standard footprint; a functional replacement would need the same 324V standoff and 1.5kW pulse rating, but the pinout is two-lead axial so any through-hole TVS in the same voltage class fits the board holes. No pin-compatible cross-reference from Vishay is published.
Through-hole mounting in a DO-201AA (DO-27) axial package. The 1.5KE supplier device package code is the same as the series name. Tape-and-box packaging suits hand-insertion or low-volume assembly. No power-line protection — this is a secondary-side transient suppressor, not a primary mains protector.