private static List<Provider> getExternalProviders(String algorithm) {
        List<Provider> providers = new ArrayList<>(1);
        for (Provider p : Security.getProviders(algorithm)) {
            if (!Conscrypt.isConscrypt(p)) {
                providers.add(p);
            }
        }
        if (providers.isEmpty()) {
            logger.warning("Could not find external provider for algorithm: " + algorithm);
        }
        return providers;
    }
Finds providers that are not us that provide the requested algorithms.
common/src/main/java/org/conscrypt/CryptoUpcalls.java