  After discussing the key idea underlying the Maxwell's Demon ensemble, we
employ this idea for calculating fluctuations of ideal Bose gas condensates in
traps with power-law single-particle energy spectra. Two essentially different
cases have to be distinguished. If the heat capacity remains continuous at the
condensation point in the large-N-limit, the fluctuations of the number of
condensate particles vanish linearly with temperature, independent of the trap
characteristics. If the heat capacity becomes discontinuous, the fluctuations
vanish algebraically with temperature, with an exponent determined by the trap.
Our results are based on an integral representation that yields the solution to
both the canonical and the microcanonical fluctuation problem in a singularly
transparent manner.
