Understanding AC to DC conversion
Small switching power supplies usually first use a diode rectifier to convert the low frequency AC from the wall to high voltage DC. This high voltage DC is then used as power input for main switching power regular. Without a special circuit called power factor correction this input circuit does not draw power continuously, but only when the amplitude of the sine wave AC reaches a higher voltage than the voltage of the internal bypass capacitors for this high voltage DC, current during this time needs to be significantly higher, because no current is flowing during the remaining time of the AC period. The input current of your power supply is likely only used if you run it at 100 V and the input current is not an average but a peak current instead. Average current is much lower, otherwise it would require active cooling to get away all the heat.

Some power is likely lost due to inefficiencies of the power supply, but efficiency at peak output current should be around 80% or better.