The STTH10R04G is a 400 V, 10 A fast-recovery rectifier from STMicroelectronics, built with standard planar technology and housed in a D2PAK (TO-263AB) surface-mount package. Its 40 ns reverse recovery time (trr) puts it squarely in the ultrafast class for a 400 V part — fast enough to keep switching losses low in a 50–100 kHz PFC boost or flyback clamp, without the snap-off characteristic of some hyperfast diodes that can ring up the node. The 1.7 V forward drop at 10 A is a typical trade-off for that speed; you trade a volt of conduction loss for the recovery charge savings.
Obsolete — the sourcing reality
10 A continuous, 175 °C junction — the thermal budget
The 10 µA reverse leakage at 400 V is a room-temperature number; expect it to multiply at 150 °C junction, so budget for that in the standby-loss calculation.