What's the difference between WS-C3650-24PS-S and WS-C3650-48PS-S ? 

Cisco 3650 WS-C3650-48PS-S Switch :

Layer 3 routing features

48 * 10/100/1000 Ethernet POE+ ports with fixed 4 * 1G SFP uplinks

390W POE power budget with up to 30W per port

IP base image with update option to IP service (L-C3650-48-S-E)

Up to 40G wireless bandwidth per switch, up to 25 APs and 1000 Wireless clients for each switching entity

Up to 9 members stacking and up to 160Gbps of stack throughput

Cisco 3650 WS-C3650-24PS-S :

Layer 3 routing features

24 * 10/100/1000 Ethernet POE+ ports with fixed 4 * 1G SFP uplinks

390W POE power budget with up to 30W per port

IP base image with update option to IP service (L-C3650-24-S-E)

Up to 20G wireless bandwidth per switch, up to 25 APs and 1000 Wireless clients for each switching entity

Up to 9 members stacking and up to 160Gbps of stack throughput