Yeah I would recommend this too. I've only used Dell Optiplex Micro series, no issues so far. They use external PSU similar to those in laptops, which helps with power efficiency.
Something with 8th gen i5 can be had for about 100-150 USD from ebay, and that's more than powerful enough for nearly all self-hosting needs. Supports 32-64gb of RAM and two SSD.
I second this, I have a 4 node Proxmox cluster running on MFF Optiplexes and it's been great. 32gb of RAM in each and a second USB NIC (bonded with the built-in NIC) makes for a powerful little machine with low power draw in a convenient package.
The Optiplexes look nice, but I went with the Lenovo m720q's for the PCIe slot ... 10Gb dual SFP+ NICs are cheap as chips on eBay and when you can migrate VM's faster it's a nice quality of life improvement for migrating VM's between proxmox nodes.
Something with 8th gen i5 can be had for about 100-150 USD from ebay, and that's more than powerful enough for nearly all self-hosting needs. Supports 32-64gb of RAM and two SSD.