Step 1: Understand the phrasal verb.
The phrasal verb call off means to cancel an event, meeting, programme, or activity that had already been planned.
Step 2: Interpret the sentence.
The sentence states that the management called off the training programme because of a sudden power outage. This means the programme was not conducted as planned.
Step 3: Analyse the options.
• (A) Incorrect. Postpone means delay, whereas call off means cancel.
• (B) Correct. It exactly matches the meaning of the phrasal verb.
• (C) Incorrect. It has no relation to the meaning of call off.
• (D) Incorrect. Rescheduling means fixing another date, not cancelling.
Step 4: Final conclusion.
\[
\boxed{\text{Call off}=\text{cancel something that was planned}}
\]
Hence, the correct option is \(\boxed{(B)}\).