Replacing torch/flashlight battery with power adapter
There is some options to choose from:

Option 1 - Lower power

Go with the 3V power supply and the torch will like still work (maybe not at full brightness)

Option 2 - Regulate it down

Get a power supply with a higer voltage and regulate it using either a linear voltage regulator or a DC-DC buck regulator.

Option 3 - Drop voltage with diode

Get the 4.5V power supply and place a diode in series, which will drop about 0.7V making it 3.8V which should be fine for the torch.