If you run into issues with "invalid object in plist for destination format", you probably have bytes-like data in the plist, which plutil does not consider serializable to json.

Python has built-in plist support, and we can specify a custom default function to specify what to do when serialization fails (e.g. on bytes). If you don't care about the bytes fields, we can just serialize them as '<not serializable>' with the following python one-liner:

python -c 'import plistlib,sys,json; print(json.dumps(plistlib.loads(sys.stdin.read().encode("utf-8")), default=lambda o:"<not serializable>"))'

This takes the stdin, parses the plist, then dumps it to json. For example, to get current power information for your Mac, you can run:

ioreg -rw0 -c AppleSmartBattery -a | python -c 'import plistlib,sys,json; print(json.dumps(plistlib.loads(sys.stdin.read().encode("utf-8")), default=lambda o:"<not serializable>"))'

and if you wanted to just get the current charging wattage, you could pipe that into jq '.[0].AdapterDetails.Watts'