### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current behaviour

See inline discussion at https://github.com/bitcoin/bitcoin/pull/26467#discussion_r1269177446

@whitslack:

> Consider the case where I am paying someone on chain under the stipulation that _they_ will eat the mining fee. (Thus, I specify _their_ address in `subtractfeefrom` when I'm constructing my transaction.) Later, they tell me that they can't wait for confirmation any longer and need an urgent fee bump. If I naïvely specify their output as the `reduce_output`, I may end up paying them _**much more**_ than I intended to if I only have large UTxOs in my wallet.


### Expected behaviour

Not sure.

Improving the docs is one option, but this behaviour seem quite counter intuitive.

My own suggestion:

> Should we disable the adding of new inputs when `reduce_output` is set? If someone really intends to do that, they should probably use `outputs`.

### Steps to reproduce

Haven't tried.

### Relevant log output

_No response_

### How did you obtain Bitcoin Core

Compiled from source

### What version of Bitcoin Core are you using?

Master after #26467

### Operating system and version

Any

### Machine specifications

_No response_
}
    std::optional<CAmount> combined_bump_fee = wallet.chain().CalculateCombinedBumpFee(reused_inputs, newFeerate);
    if (!combined_bump_fee.has_value()) {
        errors.push_back(strprintf(Untranslated("Failed to calculate bump fees, because unconfirmed UTXOs depend on enormous cluster of unconfirmed transactions.")));
    }
    CAmount new_total_fee = newFeerate.GetFee(maxTxSize) + combined_bump_fee.value();
    CFeeRate incrementalRelayFee = std::max(wallet.chain().relayIncrementalFee(), CFeeRate(WALLET_INCREMENTAL_RELAY_FEE));
    
    CAmount minTotalFee = old_fee + incrementalRelayFee.GetFee(maxTxSize);
    if (new_total_fee < minTotalFee) {
        errors.push_back(strprintf(Untranslated("Insufficient total fee %s, must be at least %s (oldFee %s + incrementalFee %s)"),
            FormatMoney(new_total_fee), FormatMoney(minTotalFee), FormatMoney(old_fee), FormatMoney(incrementalRelayFee.GetFee(maxTxSize))));
        return feebumper::Result::INVALID_PARAMETER;
    }
    CAmount requiredFee = GetRequiredFee(wallet, maxTxSize);
    if (new_total_fee < requiredFee) {
        errors.push_back(strprintf(Untranslated("Insufficient total fee (cannot be less than required fee %s)"),
            FormatMoney(requiredFee)));
        return feebumper::Result::INVALID_PARAMETER;
    }
    
    const CAmount max_tx_fee = wallet.m_default_max_tx_fee;
    if (new_total_fee > max_tx_fee) {
        errors.push_back(strprintf(Untranslated("Specified or calculated fee %s is too high (cannot be higher than -maxtxfee %s)"),
            FormatMoney(new_total_fee), FormatMoney(max_tx_fee)));
        return feebumper::Result::WALLET_ERROR;
    }
    return feebumper::Result::OK;
}
static CFeeRate EstimateFeeRate(const CWallet& wallet, const CWalletTx& wtx, const CAmount old_fee, const CCoinControl& coin_control)