A pluggable module connected to the backplane or other connection interface of an information system unit so as to provide additional functionality thereto (such as a communications interface to an electrical or fiber optics cable), and arranged to draw electrical power from the system. In order to prevent excessive in-rush current on connection, the module is provided with power control circuitry which is adapted to incrementally increase the supply voltage to components within the module in a manner so as to avoid power supply glitches in the system, such as a substantial voltage drop, and/or excessive current flow.