Your search for "A900-PWR550-A" revealed the following:
Cisco A900-PWR550-A ASR 900 Series 550W AC Router Power Supply
SKU: NSH-7840
Condition: Seller refurbished
Shipping: Overnight Options
Warranty: 365 days
$ 139.99
• 4 in stock
Call if you need more
NEW Cisco A900-PWR550-A ASR 900 Series 550W AC Router Power Supply
SKU: NSN-2914
Condition: New
Shipping: Overnight Options
Warranty: 365 days
NEW Cisco A900-PWR550-D ASR 901 Series 550W DC Router Power Supply
SKU: NSN-5775
Condition: New
Shipping: Overnight Options
Warranty: 365 days