I have a bit of an obsession getting my homelab to as low an idle as possible. It runs Ubuntu Server with Dockers for Home Assistant, Immich, NextCloud, MariaDB, N8N, Jellyfin and a few others, but rarely does any heavy lifting. It's running on a Lenovo M720q with 8GB ram, a 256GB SATA SSD, and a 1TB NVMe.  
  
To get some more bandwidth for my network drive, I decided to add a 2.5G card. I was originally running on the onboard 1G ethernet and did a lot of work to get it to idle around 4.1W, measured at the wall(long-term average). Then I added a cheap Realtek RTL8125B 2.5G card from Amazon, and the draw immediately jumped up to around 8W.

Just wanted to share the steps here that got it back down to around 4 Watt, now with the 2.5Gbit card:

After a LOT of tinkering, I found out that the main issue was with the stock driver Ubuntu Server comes with which prevented the system to go to deeper C-states. I had to fix the PCIe link power management because the NIC was keeping the CPU package awake. First, I swapped the default r8169 driver for r8125-dkms. The key part was actually configuring the r8125 driver to force ASPM on with a config file, because even with the BIOS set correctly, it stayed disabled by default. After that, I forced the powersupersave policy through a udev rule and ran a powertop auto-tune.  
  
My long-term average is now 4.29W. Slightly higher, but still very low Pretty happy that adding the 2.5G link only ended up costing me about 0.2W extra once the configuration was actually right. Given how many M720qs and equivalent I see on here, I thought it was worth the share. Anyway, if you're seeing high idle draw on these tiny nodes after adding a NIC, it's worth checking if your PCIe links are actually napping.

Got my M720q with 2.5G NIC to idle at 4.29W