Currently as of April 2024 there is no formal UL listing for PCS, only a limited “certification requirement decision” but this is changing with the new UL standard.
A PCS is a “system” of devices : controller, sensor, method to communicate between controllable loads and sources. A PCS is not 1 device. This system maintains safe levels of current and loading on busbars.
A solar plus storage system is one example. It takes power from 1 or more PV arrays, uses current transformers, communication cables. When the sensors detect a busbar is approaching overload, it will communicate with the other devices (inverter for example) to decrease power to the busbar, and send it to a battery to charge for example. If the system detects the battery is at desired charge, it may send power to to another loads panel, or back to grid.