I don't think the USB header is there to provide extra power, as the PCI-E 1x bus is already capable of powering up to 75W devices,
I did a little digging about PCIe x1 power and came up with an alternative answer. It's not 75W. That's only for longer PCIe x16 cards.
https://linustechtips.com/topic/1378385-wattage-of-1x-slot/
https://www.techspot.com/trivia/27-without-attaching-additional-power-cables-how-much-can/
1). When attached to a motherboard's PCIe x16 slot, a card such as the GeForce RTX 4080 can draw up to 75W from the +3.3V and +12V rails (3.3V x 3A + 12V x 5.5A)
2). PCIe x4 and x8 cards can draw up to 25W from the motherboard's slot
3). x1 cards are limited to 10W unless configured as a 'full-height' or 'high-power card' to pull the aforementioned 25W
I hadn't realised the 75W limit for PCIe x16 was made up of two components, namely 12V @ 5.5A (66W) plus 3.3V @ 3A (9.9W). 66 + 9.9 = 75.9W.
It would seem that PCIe x1 cards are restricted to 10W, but might be able to pull 25W. However, the PCE-AC55BT B1 is only half-height, so I suspect it's limited to 10W max.
Pins B8, A9 and A10 supply 3.3V power and pin B10 supplies 3.3V Aux power (whatever that is?). These four pins appear to be the only +3.3V supplies available on x1, x4, x8 and x16 slots and should be capable of providing 3.3A between them.
https://pinoutguide.com/Slots/pci_express_pinout.shtml
PCI-Express 1x Connector Pin-Out
| Pin | Side B Connector | Side A Connector | | |
| # | Name | Description | Name | Description |
| 1 | +12v | +12 volt power | PRSNT#1 | Hot plug presence detect |
| 2 | +12v | +12 volt power | +12v | +12 volt power |
| 3 | +12v | +12 volt power | +12v | +12 volt power |
| 4 | GND | Ground | GND | Ground |
| 5 | SMCLK | SMBus clock | JTAG2 | TCK |
| 6 | SMDAT | SMBus data | JTAG3 | TDI |
| 7 | GND | Ground | JTAG4 | TDO |
| 8 | +3.3v | +3.3 volt power | JTAG5 | TMS |
| 9 | JTAG1 | +TRST# | +3.3v | +3.3 volt power |
| 10 | 3.3Vaux | 3.3v volt power | +3.3v | +3.3 volt power |
| 11 | WAKE# | Link Reactivation | PERST# | PCI-Express Reset signal |
| Mechanical Key | | | | |
| 12 | RSVD | Reserved | GND | Ground |
| 13 | GND | Ground | REFCLK+ | Reference Clock
Differential pair |
| 14 | HSOp(0) | Transmitter Lane 0,
Differential pair | REFCLK- | |
| 15 | HSOn(0) | GND | Ground | |
| 16 | GND | Ground | HSIp(0) | Receiver Lane 0,
Differential pair |
| 17 | PRSNT#2 | Hotplug detect | HSIn(0) | |
| 18 | GND | Ground | GND | Ground |
As mPCIe/M.2 cards use 3.3V, it's better to use this exact voltage from slot, instead of adapting 5V from USB.
I didn't know these modules required 3.3V only, but confirmed you were spot on. Thanks for the heads up.
The link below to a typical WiFi/Bluetooth module shows a 3.3V supply but no mention of power required.
https://advdownload.advantech.com/productfile/PIS/AIW-165/file/AIW-165_DS(032322)20220323144214.pdf
I'd expect 9.9W from the PCIe bus 3.3V rail to be more than enough to power the WiFi card, without the need for additional 5V power from an external USB port.
I'm basing this on the fact that maximum permitted WiFi RF power (indoors) is restricted to 100mW (2.4GHz) and 200mW (5GHz). Even with the addition of Bluetooth, this still won't exceed 9.9W.
It's the USB connection that is needed in order to communicate with the BT portion of card.
I suspect this is the correct answer.
