Two voltages, one small package
The TPS3779ADBVT is a dual-voltage supervisor from Texas Instruments that monitors two independent supply rails and asserts a single active-low reset when either falls below its threshold. The thresholds are adjustable via external resistor dividers, so the same part can handle mixed-voltage systems — say 3.3 V and 1.8 V, or 5 V and 2.5 V — without needing a different supervisor for each rail.
What the 125°C rating means for your board
For most applications the output is lightly loaded (driving a CMOS reset input), so self-heating is negligible and the full 125°C ambient is usable.