OK, thank you for the answer, I'll try asking the same in nopCommerce forum. It's weird though that regular price is not shown together with discounted one...
Yes, you are right. For example on our website (at the time of writing Nop-Templates.com runs on nopCommerce 3.90) we have modified the code to show the old price and the discounted price when using discounts (not old/new price).
So is it possible to share the code you applied? I use 4.00 but it doesn't matter.