The HP T620 Plus thin client I had been using as my primary OPNsense box and router died unexpectedly. I went to work as usual in the morning around 7 am, and by the time I got home around 5 pm I returned to find my internet connectivity completely offline. The T620 Plus was off and unable to be powered on. I tried a different 19.5V power adapter to no avail. I attempted to perform some basic troubleshooting including cleaning out the dust, attempting to power on with RAM/SSD and PCIe ethernet card removed, but my attempts were futile. Rather than spend more time, energy, and money trying to troubleshoot with replacement parts, I decided to write it off as a loss and go in search of some replacement hardware. (When I have time and get around to it I'll throw the broken unit on eBay at a steep discount for anyone who wants to try fixing it.)
In the meantime, I went in search of some low-priced x86 hardware that could serve as a reasonably performant replacement platform. I had been eyeing the PC Engines APU2 for some time, but the price after accounting for a case, SSD/SD card, etc. (~$150-160 + shipping) was a little higher than I wanted. Additionally, I wanted to repurpose the still-functional network card from my old T620 Plus box, a dual-port half-height Intel I340-T2. After some eBay browsing I came across numerous listings for used/refurbished small-form-factor (SFF) business/enterprise PCs from Dell/HP/Lenovo. In the sweet spot of $75-100 there were an abundance of listings for complete or near-complete machines with circa 2013/2014 Haswell-generation CPUs. I ended up finding a nice listing for a refurbished Dell OptiPlex 7020 equipped with a Core i3-4160 3.6GHz CPU rated at a TDP of 54W and 8GB of DDR3-1600 RAM. After some negotiating with the seller I picked it up for $68 shipped. The unit no longer had any SATA storage so I ended up snagging a used 64GB SanDisk X110 2.5" SSD for about $13.50 shipped.
When I unpacked the Dell a few days later, I found it to be in excellent condition - no scratches or dents anywhere on the chassis. Looking up the Dell service tag, the warranty expired in 2018. Thanks to its toolless, IT-friendly nature installing the SSD and network card was a piece of cake. There is a 3.5" drive cage but with no formal way of mounting a 2.5" drive, at least with extra screws, but thanks to the cramped nature of the system the SSD is still quite secure just casually sitting inside the drive cage. After a minor issue with improperly-seated RAM preventing it from booting, the Dell fired right up. The installed BIOS version - A04 - did turn out to be quite antiquated, but updating it to the latest A18 revision from 2019 was a smooth affair via USB. After configuring the machine to boot in UEFI mode, OPNsense installation went without a hitch.
The OptiPlex 7020 has been running great and is near-silent although it technically has a couple of small-diameter fans on the CPU heatsink and in the front. Temperatures on the dual-core i3-4160 are around 36 C at idle and it rarely exceeds that in a room kept around 73 F. Obviously, with the socketed desktop-class CPU power consumption will be higher than the embedded AMD CPU in the T620 Plus, but should still be reasonable with the relatively low 54W TDP of the i3-4160.
Once I have a chance to hook up a watt meter I will be sure to update this post with formal readings. With power management enabled in hiadaptive mode, idle power is about 25W at the wall, an increase of 7W from the T620 Plus. This can be lowered further to ~23.5W or so by setting the power management mode to "minimum" and unplugging the power cable to the optical drive. In any case, this platform is substantially more powerful than the anemic-by-comparison AMD GX-420CA in the T620 Plus.
UPDATE: Curious to see what effect upgrading to a low-power T-series CPU would have, I snagged an i3-4160T (3.1GHz, 35W TDP) from eBay and swapped it in. Idle power consumption was essentially identical, although peak load wattage dropped slightly to 40-42W from about 45W. The 500MHz deficit in base clock compared to the standard i3-4160 is reflected by a slightly lower PassMark score, but make no mistake, the i3-4160T still packs plenty of power to run pfSense along with add-ons. If you do go for a replacement Haswell CPU in your 7020, I recommend avoiding the even-cheaper Celeron and Pentium chips as these lack AES-NI.
Overall, I'm very satisfied with this new-to-me replacement hardware, which was probably a lightly-used office PC from some random company in its past life before it went off-lease and was refurbished. Thanks to its relatively strong CPU (at least for consumer-grade routing purposes) it should be more than powerful enough to handle gigabit-class internet, as long as nothing physically breaks.