Thanks for your help. I followed your advice and entered the refund using the Credit Card Charges option and that shows up under the supplier. I deleted the original credit transaction as well, because I noted that the credit card charge didn't change the supplier balance.
Usually where I have received a supplier credit note for items that I returned, that amount would be deducted from my next payment to them so my usual way of entering a credit Bill will still work for me I think. I just use the credit amount against an invoice when paying it...
The other scenarios look more complex so I think I'll need to read that in detail to fully understand it. Although that hasn't happened (yet) I will need to take time to fully understand how to process it.
Thanks again for your help.