I think that component is an LDO regulator. It getting hot might indicate excessive voltage from your supply.
It is also near the F3 polyfuse (look underneath the board toward the corner, you'll see the F3 label).
If the PSU is unregulated it can also output too high a voltage, which may trigger the overvoltage device in the PI, which will
temporarily short the 5V to ground, this will then "blow" polyfuse F3,
which will take several days to recover from. Meanwhile (possibly with
another PSU) the PI might not get enough power because the (partly)
blown polyfuse is consuming some of the power. The solution is when
this happens to ways a few days to give the polyfuse time to recover
before attempting to use the better PSU. If you suspect a blow
polyfuse, measure the voltage across F3, which should be less than