Hii,

1. Make sure supplier product codes exist for each product variant (not just on the product template) in Purchase > Products > Suppliers tab.
2. Add this domain to the delivery order line’s product field or customize the picking report to show the variant’s default_code (which is unique per variant).
3. For showing correct supplier product code on delivery orders:

​Create a computed field on stock.move.line to get the supplier code for the specific variant and supplier:

from odoo import models, fields, api

class StockMoveLine(models.Model):

    _inherit = 'stock.move.line'

    supplier_product_code = fields.Char(compute='_compute_supplier_product_code')

    @api.depends('product_id', 'move_id.picking_id.partner_id')

    def _compute_supplier_product_code(self):

        for line in self:

            supplier = line.move_id.picking_id.partner_id

            if line.product_id and supplier:

                info = self.env['product.supplierinfo'].search([

                    ('product_id', '=', supplier.id)

                ], limit=1)

                line.supplier_product_code = info.product_code if info else False

            else:

                line.supplier_product_code = False

Update your picking report or picking view to show supplier_product_code instead of default product code.

This will ensure the delivery order lines show the correct supplier product codes per variant.