What this TVS diode does on the board
The 1.5KE300CAHA0G: It clamps transients at 414 V max while conducting 3.8 A peak pulse current, protecting downstream silicon from overvoltage events on a 256 V nominal rail.
Clamp voltage and rail protection
When a transient exceeds the breakdown threshold, the Zener clamps at 414 V max — that is the voltage the downstream capacitor and IC see during the surge. The 3.8 A peak pulse current rating tells you the diode can sink that much current through the avalanche without failing short.
Housed in a DO-201AA (DO-27) axial-lead package, it mounts through-hole. The 0.052-inch lead diameter fits standard 0.040-inch plated through-holes; the body length is about 0.4 inches. On a double-sided board, the leads are clinched and soldered on the bottom side — the axial form factor is still common in power supplies and automotive junction boxes where the diode sits off the board with a heat-shrink sleeve.
This is a current-production part, not a discontinued line.