You can buy anything else in Walmart with a Walmart Gift Card but you cannot buy a prepaid Visa Gift Card or any other prepaid card with the Walmart Gift Card.
Walmart doesn't make much commission on Prepaid Visa Card sales so they want you to use only the Walmart Gift Card for only purchases in their stores so they make a profit.
You can however sometimes sell the Walmart Gift Card online for cash or other prepaid cards that you can use anywhere.