If I incorporate a UL/NRTL listed power supply in our product, must we re-test?
THIS IS ONLY AN OPINION AND IS NOT AUTHORITATIVE IN ANY WAY. THIS DOES NOT CONSTITUTE "ADVICE"

In my past experience, simply using a listed power supply does not grant you immunity from the listing/compliance process.

It is possible that using a fully-enclosed, finger-protected supply like an ATX-style will make your testing extremely easy -- using a wall-wart style would make it even easier -- but I would very much suspect that you can't "claim UL listing" just by using one.

Unlike CE mark, UL, RTL, etc are not self-certifications.