We have an old HP C7000 at work. It pulls 423W empty, 560W with a single blade. Safe to say it's a bad idea.

But regarding your question: You already have the thing, so measure it for actual use, as your workloads will most likely vary over time. Or to calculate: E(kWh) = P(W) × t(hr) / 1000, so 3833.025(kWh) = 5250(W)x730.1 The number of hours per month is an average over a year.

Network stack: UDM-Pro, USW-Agg, USW-16-PoE, Raspberry Pi for DNS, VPN & monitoring, U-LTE-Pro, USW-Flex, G4-Bullet, 2x UAP-AC-Mesh, 2x UAP-AC-LR, 1x UAP-FlexHD sitting on a 500 VA UPS pulling ~100W.

Homeserver (24/7) is a Ryzen 3700X-system with 13 HDDs usually pulling around 150W on it's 1000VA UPS.

Power is quite expensive here in Germany, but the cost of small solar-setups is dropping, so I might setup a little PV-installation to offload costs. Would probably allow me to run more servers again^^