A metered PDU shows the load on its own display, so you know how much of a 20A or 30A circuit is left before adding another server or switch. The two APC models here are 120V with 5-20R outlets: the AP8830, a 0U vertical strip with 24 outlets, and the AP7802B, a 2U unit with 16 outlets on a 30A circuit.
If you also need to turn outlets on and off remotely, see switched rack PDUs, or read metered vs switched PDUs.
