From the author:
GPU Core Power covers only the core rail of the GPU (measured via VRM telemetry). GPU chip power should cover entire GPU chip power (core + aux + additional logic), which is calculated by the GPU and partially measured (core and sometimes aux too) and partially estimated based on activity counters (additional logic) or fixed constants. Note, that the core power might sometimes seem higher, due to instantaneous peaks, which are averaged in the total (chip) power calculation.