As servers are equipped with more memory modules each with larger capacity, main-memory systems are now the second highest energy-consuming component in big-memory servers and their energy consumption even becomes comparable to processors in some servers. Meanwhile, it is critical for big-memory servers and their main-memory systems to offer high energy efficiency. Prior work exploited mobile LPDDR devices' advantages (lower power than DDR devices) while attempting to surmount their limitations (longer latency, lower bandwidth, or both). However, we demonstrate that such main memory architectures (based on the latest LPDDR4 devices) are no longer effective. This is because the power consumption of present DDR4 devices has substantially decreased by adopting the strength of mobile and graphics memory whereas LPDDR4 has sacrificed energy efficiency and focused more on increasing data transfer rates; we also exhibit that the power consumption of DDR4 devices can substantially vary across manufacturers. Moreover, investigating a new energy-saving feature of DDR4 devices in depth, we show that activating this feature often hurts overall energy efficiency of servers due to its performance penalties.