DI Boxes perform several important functions: they are designed for impedance matching and balancing the signal of a guitar, a keyboard or any line-level output source, and for injecting directly the signal with very long connections to the XLR microphone inputs of a mixing console.
D10A is an active direct box with transformer and requires the phantom power to work. The advantage of a transformer is the possibility to avoid any electrical connection between the sound source and the mixer. This provides two huge benefits: with no electrical path, ground loops are eliminated and the cancellation of common-mode noise, like hum, is possible. The advantage of active instead of passive DIBOX is null insertion loss and less output hum and noise.