No! It is not!! :O
Using a PowerBook 165 adapter may work temporarily, but there's a good chance that doing so will cause damage to the power circuits on the Portable's logic board.
The reason for this is the Portable is designed to run only off the main battery, and the proper Portable adapter is, in effect, a trickle charger for the main battery so it maintains a full charge while the Portable is in use. This is why they won't power on without a functional main battery installed, even if the (proper) adapter is plugged in.
That being said, it is strongly recommended that you use ONLY the proper adapter and fully charged battery (which is easier said than done, as many original batteries are now dead and need to be rebuilt with new cells).
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