1) With combination of WS-CAC-1000W and WS-CAC-3000W, is WS-CAC-3000W hot-swappable? should be yes?
A; YES
2) When the power supply 2 is inserted, would it causes a downtime? should be no?
A: NO
3) based on the website(http://www.cisco.com/en/US/customer/products/hw/switches/ps708/products_installation_guide_chapter09186a008020e0d3.html#wp1030022), I believe I am still able to get a power supply redundancy with both WS-CAC-1000W and WS-CAC-3000W? should be yes?
A: YES, Any combination of PS types will operate together (including mixed AC and DC input types), though Cisco do not recommend this as a standard operating practice.
The key caveat for this situation is that the customer needs to treat the configuration as if both units are of the lower output rated type. (See that link you referenced).
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