As Balaji already noted, the current master will "sync" the current config with other stack members joining the stack. BTW, "sync" in this case means the master's config will effectively replace/overwrite the new stack member's config.)
This also applies if, in your example case, the stack member that was powered off was the stack master. Further, even if that stack member has a higher priority than the stack member that kept running, and took over the role of stack master, the former stack master won't preempt the current stack master. If that member loses power, then the former stack master (again in your two member stack example) will take over again as stack master, but also again, using the config it obtained from the then active replacement stack master.
One situation where the configs may not exactly "sync" up is if the switch member that lost power is replaced by another physical switch. In such a case, what happens depends on whether the replacement switch has been provisioned with the stack member number of the switch that failed and assuming it's like hardware, it will come on-line just as the former powered off switch would have.
However, if the switch is not provisioned like the former switch or of like hardware, if will not come on-line exactly as if the prior switch would have. This applies whether you've made additional configuration changes or not.
PS:
An example of "unlike" hardware, original switch has 24 ports and replacement has 48, or the converse. Or, original switch has FE ports and replacement has gig ports, or also the converse.
