The Type A adapter is designed to support any USB 2.0 or 3.0/3.1 Type A male cable, and in testing, it did. This included a third-party ethernet adapter that required a Yosemite-compatible driver, discussed in the next section.
Apple's multiport adapters are ungainly, looking like tiny manta rays, but perfectly functional. Each has a USB-C power-only passthrough port and a USB 3.1 Gen 1 Type A female port just like on the simple adapter. The center port is either HDMI or VGA. (The ungainly formal names for each $79 adapter are the USB-C Digital AV Multiport Adapter and the USB-C VGA Multiport Adapter.)
I tested the HDMI adapter with both an HDMI-to-DVI and HDMI-to-HDMI cable, and each worked just as expected with an Asus VG248QE, a 1080p (1920 by 1080 pixels) with HDMI 1.4, DisplayPort, and dual-link DVI-D inputs. The VGA adapter also tested as expected with a Dell monitor with native VGA support.
I did not have a 4K monitor on hand to test. Apple says resolutions of 3840 by 2160 at 30Hz and 4096 by 2160 at 24Hz are supported, and reports elsewhere indicate mixed results with 60Hz monitors or monitors in a 60Hz mode.
The USB Type A converter works as expected as well with all the cables I tested it with, including some uses I didn't expect below.
DisplayPort, USB Type A, and ethernet
Apple's MacBook launch included some confusion, because the company said that the USB-C port it included had "native" DisplayPort 1.2 video output. But Apple neither sold such an adapter, nor has it apparently announced any plans to do so.
It fell to arch-rival Google, which just a few days later announced a USB-C to DisplayPort cable ($40). I tested it with the same Asus monitor above, and it again performed as expected: it worked with no flickering or interface, and setting up multiple monitors on the MacBook through the Displays preference acted as I expected. (A nifty advantage of a multi-port input monitor is connecting multiple Macs through different methods, leaving cables attached, and switching as needed.)
While I acquired both USB-C to USB 2.0 Type A and 3.0 Type A cables, these are trickier to test, because of Apple's limited support for USB-based transfer, except with Migration Assistant and Setup Assistant. The 2.0 cable won't work at all between Macs, and because it's a Type A connection at the end, it typically can only plug into "host" devices, like a computer. Printers, drives, and other peripherals almost always sport a square Type B port.
Apple says that Target Disk Mode is supported with a MacBook over USB so long as the cable is USB-C to Type A 3.0 or 3.1. However, with such a cable, I could not get it to work. This may be a firmware issue in the MacBook's controller or a cable issue, and I'll be testing this further. (The cables tested were Cable Matters USB-C to Type A 2.0 [$13] and an unbranded USB-C to Type A 3.0 cable [$11].)
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