The Center of Power is the centre of the Spellbinder's Castle, and it fills the entire cellar. It serves power regulation and recharge purposes.
The Center supplies the entire castle with the necessary energy, and it is also used to recharge the power stones. The stream is apparently generated by a gigantic power stone, and then made available to the entire castle. In the cellar itself stands an arched-shaped scaffolding which is always live, and if power stones on a rolling cart are pushed under the scaffolding, a flash goes into them and recharges them. It is not known how this process occurs and if external control is employed, but the device does not harm operators which frequently enter and exit, swapping out charged power stones for empty ones. The operators also don't seem to wear any specific protection against the device, which suggests that the device is not harmful to organic matter, and only selectively affects Spellbinder technology.
The steel scaffolding is live and unprotected - a fact which Paul exploits in episode 11: when Ashka faces him in her power suit, he throws a steel pole into the scaffolding, causing a short and massive disruptions to the entire power grid. Ashka with her power suit are magnetically drawn and attached to the scaffolding, which further disrupts power flow within the device, causing visible signs of trouble and making everyone run from the castle.
Once Ashka is separated from the scaffolding, the device resumes normal operation. Also, Ashka herself, and her suit, seem mainly unharmed by this prolonged contact with the power grid, which suggests that the device itself runs on very high voltage, but sufficiently low current.