>or more important question is there an easy way to get over the
>limitation? so I can take advantage of the 110Vac selection in
>240Vac line to get a few more AC output.

short answer you cannot.

The reason is the primary of the 110V winding does not have enough
inductance to limit the current to a safe value, and so the transformer gets
hot and burns out - as you have discovered.

However, as you apparently have an endless supply of these wall warts, you
could use two, with the secondaries in series - just do not unplug one and
put your fingers across the pins.

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