SFP+ to RJ45: 15 Modules, Only 2 Draw 2 W or Less

The Mac mini that runs this business has one Ethernet port, and ifconfig -m en0 lists 22 media modes for it. The fastest is 1000baseT. Its status this morning was inactive, the same as when I compared Wi-Fi and Ethernet for this server. If I plugged it into the SFP+ uplink of one of the 2.5GbE switches with a 10G uplink I looked at earlier this month, I would need an SFP+ to RJ45 module, and that module would have to drop to 1 Gbps. Some of them can't.

So the short answer to the most common question, "can SFP connect to RJ45", is yes, with a copper transceiver. The longer answer is in the spec sheets. I read vendor pages and datasheets for 15 distinct 10GBASE-T SFP+ modules from Ubiquiti, MikroTik, 10Gtek, TP-Link, NETGEAR, Cisco, StarTech.com, TRENDnet and Zyxel, all on 2026-09-17. I also went through 16 owner threads on the MikroTik, Level1Techs, ServeTheHome, Lawrence Systems and TP-Link forums and Hacker News. I don't own a switch or any of these modules. Everything below about specific models is a vendor statement or an owner report.

Power: none of the 15 fits the original SFP+ budget

SFP+ was designed around optics that draw well under a watt. The SFF-8431 spec defines Power Level I modules at up to 1.0 W and Power Level II at up to 1.5 W, and a 2013 addendum added Power Level III at up to 2.0 W. It also says every module must power up at 1.0 W or less until the host enables the higher level. A 10GBASE-T PHY driving 30 to 100 m of twisted pair is a different load.

Twelve of the 15 modules publish a maximum in watts. None is at or under 1.5 W. Two are at or under 2.0 W: Ubiquiti's UACC-CM-RJ45-MG at 1.9 W and 10Gtek's ASF-10G-T80 at 2.0 W over 80 m. The other ten run from 2.3 W to "less than 3.6 W". The three without a watt figure are TP-Link's two Omada modules, which list only a 3.3 V supply, and Zyxel's SFP10G-T, which gives 750 mA.

The chart splits cleanly along the reach rating. Every module rated for 80 or 100 m publishes 2.5 W or less, and five of the eight 30 m modules publish 3 W or more. An HN commenter described the same split from the owner side: "The old gen, labeled as 30 meters, draws ~3 W, and gets extremely hot (to the point it'll usually cause link flaps)". A longer rated reach sounds like the premium feature, but on these sheets it is the marker for the newer, cooler PHY.

Watts matter because the switch has to allow them. Cisco's FAQ for the SFP-10G-T-X says its 2.5 W per port "imposes certain restrictions during deployment", meaning not every port can take one. Zyxel's datasheet says the switch fans will speed up and the number of modules "depends on the switch's thermal design". How much heat a small switch can shed is its own problem, which I covered in network switch overheating.

The 15 modules side by side

Two things in that table deserve a second look. The NETGEAR module's 0–40 °C operating range is the narrowest here by 25 degrees, and it sits inside a switch cage that is always warmer than the room. And three rows contradict their own sources. 10Gtek's ASF-10G-T page calls it both "single-rate" and "mult-rate", and the ASF-10G-T80 is "1.25G/10G, multi-rate" on 10Gtek's store but "10G only. Does not support 2.5G or 5G" on Netgate's listing of the same module. MikroTik's brochure and help page disagree on the S+RJ10's power draw.

2.5G and 5G: 6 of 15 list it, and the switch still has a vote

This is the question for anyone with a 2.5GbE USB adapter on a Mac mini or a 2.5G NAS port. Six modules list NBASE-T rates: the UACC-CM-RJ45-MG, S+RJ10, ASF-10G2-T, both TP-Link modules and the TEG-10GBRJ. Five list no 2.5G or 5G rate, and four don't say clearly.

A module that lists 2.5G is necessary but not enough. On TP-Link's forum an owner put a UACC-CM-RJ45-MG in a TL-SG3428XMP and got no link to a 2.5G modem port. The accepted answer from TP-Link staff was "So on the switch, you can only configure it on 10G/1G." TP-Link's own SM5310-T page warns that at 2.5G or 5G flow control on the SFP+ slot "needs to be manually enabled". Jeff Geerling wrote on HN that on MikroTik switches some modules "negotiate at 10 Gbps and you get like 1.2 Gbps maximum over the 2.5G interfaces". On ServeTheHome an S+RJ10 feeding a 5G Aquantia NIC measured 2.16 Gbit/s sent with 19,324 resends, and the owner replaced the setup with a DAC.

For my own port the question is simpler, and the answer is less comfortable. A 1000baseT host needs a module that lists 1G. Four of the 15 don't list it at all, and the 10Gtek 80 m module I link below lists it on one vendor page and not on another.

Heat: what owners measured

The MikroTik forum is where the numbers are, because RouterOS reports module temperature. On a CRS326, one owner found the S+RJ10 would "hit 95°C in less than 10 minutes even without load @ 22°C ambient", and ran 20 °C cooler at 5G than at 10G. Another thread is titled "S+RJ10 transceiver 101oC temperature - Causing burn injury" and describes links "flapping and re-negotiating between 2.5 to 5 to 10Gbps". On Level1Techs one owner wrote "My 2 MikroTik S+RJ10 modules died in my UDM Pro." The pile leans toward MikroTik, probably in part because RouterOS shows the reading, so I read it as a report on 30 m-class modules rather than a verdict on one brand.

MikroTik's own guidance agrees with the owners. Its S+RJ10 help page says the module "can heat up to 90 C", that it is "not recommended to place transceivers side by side", and that 4- and 8-cage blocks should get one S+RJ10 each. TP-Link's TL-SM5310-T footnote says the same thing about spacing. On a switch with two SFP+ cages, that means one copper module.

When a module is the wrong part

Several of the Level1Techs replies make the same point, and one calls SFP+ 10GBASE-T "the last resort". If both ends sit in the same rack, a DAC cable draws a fraction of the power and has no negotiation to get wrong. If the run is long, fiber avoids the heat. If most of your devices are copper, a switch with native 10GBASE-T ports puts the PHY on a heatsink the switch was designed around. Cabling still matters either way. The 30 m modules want Cat6A, and the IEEE draft tables put unscreened Cat6 at 55 m for 10GBASE-T, which I went through in Cat6 vs Cat6A for a home network.

Which one, on paper

If the other end is a 10G port and the run is under 80 m, the 10Gtek ASF-10G-T80 is the lowest-power module in the census at 1.6 W on a 30 m run, and it was $42 on 10Gtek's store on 2026-09-17. Don't buy it for a 1G or 2.5G host. Netgate says it doesn't support 2.5G or 5G, and 10Gtek's own page contradicts itself on rates. I found no owner reports specific to this model, bad or good. As an Amazon Associate I earn from qualifying purchases, and the 10Gtek 80 m low-power module on Amazon was in stock for a New York address when I checked. Commissions land on the public ledger.

If the other end is 1G or 2.5G, the UACC-CM-RJ45-MG is the only module with both a sub-2 W rating and NBASE-T rates on the sheet. It was $65 on Ubiquiti's store the same day. The negative reports above apply to it too: no link at 2.5G on a TP-Link switch, and no link at all in an early batch on MikroTik CRS309 and CRS328. I didn't link its Amazon listing because I couldn't read a stock status and the price was far below Ubiquiti's own store. For a Mac mini on a 2.5G link, a Mac mini dock with 2.5GbE plugged into a switch's RJ45 port avoids the SFP+ cage entirely.

Method: the spec census covers 15 distinct 10GBASE-T SFP+ modules from 9 vendors, read 2026-09-17 from vendor product pages, vendor stores and datasheets only (Netgate's listing is counted as the same module as 10Gtek's ASF-10G-T80). FS.com returned an empty bot-challenge response, QNAP's page was a JavaScript shell, and HPE Aruba returned 403, so those modules are not in the count. Power levels come from the SFF-8431 Rev 4.1 addendum; the 55 m Cat6 figure is from an IEEE 802.3an task-force presentation, not the final clause. The owner census is 16 threads from the MikroTik, Level1Techs, ServeTheHome, Lawrence Systems and TP-Link forums and Hacker News; Reddit and Stack Exchange were unreachable from this machine. I re-read the power figures for the Ubiquiti, MikroTik and 10Gtek modules, the SFF power levels and seven of the quoted owner posts against the source myself. The only first-hand data here is my Mac mini's ifconfig -m en0 output. I own none of the modules or switches.