Hi stephan,
The following 24V power supplies meet your requirements of 24V, at least 3A, 2.1mm x 5.5mm output connector and are rated NEC Class 2 (part of the UL 1310 standard).
All of the following are rated for 3.75A at 24V and are part of the Globtek GTM96900P90vv series:
- TR9KI3750CCP-IM(R6B) Class II rated (no earth ground) IEC 320-C8 input connector
- TR9CI3750CCP-IM(R6B) Class I rated (earth ground) IEC 320-C14 input connector
- TR9CI3750CPCIMR6BLPS Class I rated (earth ground) IEC 320-C14 input connector with additional IEC 62368-1 “Low Power Source” rating