What type of encoding format is supported when importing an end-user certificate with a private key?

The correct choice, PKCS#12, is specifically designed for bundling a private key along with its associated certificate into a single file. This format is commonly used for importing and exporting certificates and private keys securely. It is widely accepted in various applications and systems because it can encrypt the private key, providing an additional layer of security.

PKCS#12 files often have extensions such as .p12 or .pfx, making them easily identifiable. This format allows for a straightforward import process into devices, including firewalls like SonicWall, which streamlines certificate management and deployment.

Other formats like X.509, PEM, and DER either pertain solely to the certificate or the encoding form of the data but do not inherently support that combination of a private key with its certificate in a secure bundled manner. For example, while PEM and DER are encoding formats that can represent certificates or keys, they do not natively handle both as a single file with encryption and password protection like PKCS#12.