Look for a brand logo on the physical device. Brands like PAC , Autonics , or Kikusui often use similar numbering conventions for their Operation Manuals . APC-1011 | Autonics
If this refers to a power supply or UPS system, the APM Technologies Download Center provides manuals for high-power programmable DC and AC sources. Panel PCs and Controllers: A similar product code, Download APCmaus511 pdf
For serial-to-ethernet or gateway devices (like the Look for a brand logo on the physical device
Often, "APC" is a prefix added by a specific distributor. Search for just "M511 manual" to find the original manufacturer’s datasheet, such as the IPS511 Power Switch or the MACOM A511 Amplifier Download APCmaus511 pdf