I read a short story in the 90s (but possibly much older) based on Berserkers as created by Fred Saberhagen.
AFAIR the occupants of a salvage ship had retrieved a smallish device/craft of unknown origin. It is heavily damaged and not working.
A berserker had then shown up, and (totally unprecedented to crew's knowledge) opened communication with the occupants of the ship, promising their safety if they surrendered the device. One of the workers on the ship attaches the device to power and they discover it is self-repairing (only having lacked a power source with which to do that). They further suspect it could be valuable against the berserker itself, and that is what prompted the strange behavior.
They stall the berserker long enough to get the smaller device 'mostly' repaired, but decide not to push their luck, ejecting it from the ship before making a run for it. As they leave, and the story is ending..
..the device winks out of existence on one side of the berserker, only to appear on the other & attack it from behind. It has hyper-space jump technology that the berserker lacks!
Can anyone name the story? I'm not sure if it was by Fred Saberhagen himself, or one of many other authors writing in (or out) of canon. I read it in an anthology which I have since misplaced.