Newer devices have multiple power_supply devices in sysfs:
$ grep ^ /sys/class/power_supply/*/type
/sys/class/power_supply/AC/type:Mains
/sys/class/power_supply/BAT0/type:Battery
/sys/class/power_supply/ucsi-source-psy-USBC000:001/type:USB
/sys/class/power_supply/ucsi-source-psy-USBC000:002/type:USB
There are two "USB" Type-C ports than can supply power and both are
aggregated into the "Mains" power supply by the firmware. The "Battery"
also counts as a power supply, but is missing the online attribute.
The -f check with a wildcard pattern results in an error, when multiple
devices are present:
/lib/rc/bin/on_ac_power: line 21: [: too many arguments
When the power_supply class is registered, check for a "Mains" device.
Fixes#427.
63955056ec