Can a 140 amp alternator handle a 250 watt amp?

Answer 1

yea. it's not very big really. Of course you gotta consider everything, like headlights, ac and blower, whatever, but basically speaking ohm's law is

Volts times Amps equals Watts.

or watts divided by volts equals amps.

so theoretically about 2 amps.

Of course nothing is totally efficient so there is some loss in the system, so 2 or even 3 amps is a small amount compared to the total