Does the adapter support audio transmission as well, and if so, what audio formats are supported?

Yes, the adapter supports audio transmission, including up to 8 channel LPCM, compressed audio formats like AC-3 and DTS, and HBR audio format.

What is the maximum resolution supported by the Nippon Labs 30DP-HM200-4K DisplayPort to HDMI adapter?

The maximum resolution supported is 4K x 2K at 30Hz.

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Nippon Labs 30DP-HM200-4K DisplayPort to HDMI 4K Audio / Video Converter - DisplayPort 1.2 to HDMI Adapter for DP-enabled Computers - 4K x 2K@30Hz

Support DisplayPort 1.2a input and HDMI 1.4b output.
Support HDMI resolutions up to 4K x 2K@30Hz.
Support multiple color format: RGB 6/8/10/12-bit per component (bpc) and YCbCr4:4:4, YCbCr4:2:2,8/10/12bpc.
HDMI1.4b compliant with maximum data rate 3.0Gbps.
Support up to 8 channel LPCM, compressed audio (AC-3, DTS) and HBR audio format.
Support up to 192 kHz audio frame rate and up to 24-bit audio sample size.
Integrated both HDCP Rx and Tx keys to support HDCP repeater.
Powered from DisplayPort source.