snmpwalk -v1 -c public <YOUR_APC_IP_ADDRESS> -m all
Are you positive that your device actually uses "powernet405.mib"? It's seems like this is a MIB used for SNMP traps, so you are not going to be able to snmpwalk it.
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Did not find 'enterprises' in module RFC1155-SMI (/usr/share/snmp/mibs/nsascsi.mib)
Unlinked OID in HPNSASCSI-MIB: hp ::= { enterprises 11 }
Unlinked OID in CPQIODRV-MIB: compaq# ::= { compaq 0 }
Did not find 'compaq' in module CPQHOST-MIB (/usr/share/snmp/mibs/cpqdceeo.mib)
Did not find 'ifIndex' in module RFC1213-MIB (/usr/share/snmp/mibs/cpqdceeo.mib)
Did not find 'ifDescr' in module RFC1213-MIB (/usr/share/snmp/mibs/cpqdceeo.mib)
Did not find 'sysName' in module RFC1213-MIB (/usr/share/snmp/mibs/cpqdceeo.mib)
Did not find 'sysDescr' in module RFC1213-MIB (/usr/share/snmp/mibs/cpqdceeo.mib)
Did not find 'sysContact' in module RFC1213-MIB (/usr/share/snmp/mibs/cpqdceeo.mib)
Did not find 'sysLocation' in module RFC1213-MIB (/usr/share/snmp/mibs/cpqdceeo.mib)
Based on the error, it looks like you may be using a mib that requires non-free mibs that are no longer packaged with snmp rpms. The other option appears to be adding a -M /usr/share/snmp/mibs/ to the snmpwalk command. This forces the directory and with the -m all command will include all mibs located there.
Nagios-Plugins maintainer exclusively, unless you have other C language bugs with open-source nagios projects, then I am happy to help! Please pm or use other communication to alert me to issues as I no longer track the forum.