Thunderbolt is basically external PCIe, so this is not so surprising. High speed NICs do consume a relatively large amount of power. I have a feeling I've seen that logo on the board before.
I don't know how to measure the direct power impact on a MacBook Pro (since it's got a battery), but the typical power consumption of these cards is 9 W, not much more than Aquantia 10 GBit cards.
Also, if you remember where you saw that logo, please let me know!
JFYI, for measuring power draw, you might be able to use `macmon`[0] to see the total system power consumption. The values reported by the internal current sensor seem to be quite accurate.
Speaking of hardware, the RTL8159 (10Gbps) hit the market late last year and is said to consume only about 2–3W. It apparently runs very cool compared to older chips. (Though it would need to be bonded to reach 25Gbps ;-)
I got me one of these adapters (RTL8127AF TXA403, with SFP+ cage); I haven't properly benchmarked it yet.
There's no driver support on macOS, and for Linux you'd need a bleeding edge kernel. Just trying to physically connect it (along with a connected SFP28 transceiver) to my Mac's Thunderbolt port using an external PCIe-to-TB adapter, macmon tells me a power draw of around 4.3 W, so it's not significantly less for half the bandwidth, but the card doesn't get hot at all.
Plus 1-2.5w per active cable. You need the heatsinks as the cx4 cards expect active airflow, and active transceivers as well.
I have a 10gbit dual port card in a Lenovo mini pc. There is no normal way to get any heat out of there so I put a 12v small radial fan in there as support. It works great at 5v: silent and cool. It is a fan though so might not suit your purpose.
It isn't. There is no sense in which "Thunderbolt is basically external PCIe". Thunderbolt provides a means of encapsulating PCIe over its native protocols, which puts PCIe on the same footing as other encapsulated things like DisplayPort and, for TB4 and later, USB.
