An adapter bracket, which screws onto an existing neutral bar in a load center, having legs inserted through the holes in the neutral bar or screwed into the top of the neutral bar. The adapter bracket is configured to accept downward-facing or sideways-facing plug-on neutral mounting clips of a plug-on neutral circuit breaker. The bracket has a support portion extending along a Z-axis perpendicular to a rear wall of the load center. The downward-facing clips can be plugged onto the support portion. Sideways-facing clips are received onto tabs that are bent away from the support portion of the bracket and feature chamfered ends and a relatively small aspect ratio relative to the length of the mounting clip. The other holes in the existing neutral bar remain unobstructed so that a conventional neutral conductor can be inserted through the free holes while the adapter bracket accommodates plug-on neutral mounting clips.