Vadimkut, I am not seeing a kit available to convert from non redundant to redundant power supplies, nor am I certain you can convert after the point of sale.  
Hello, We have a pretty base level T420 server which had a single non-redundant power supply and 4x slot 3.5" hard drive bay without a backplane. One day the power supply went down due to power surge. Looking online I figured that buying a new single power supply would cost about $500 which did not make sense. At the same time I found a redundant kit with 2 power supplies for a quarter of the price and I got it. When I installed it I found that the redundant power supply kit does not have PSU P4 connector which would be a power for the hard drives and the DVD drive. Instead there is a Backplane Connector (BP) which can't be used at the time. My question: is there any conversion from BP to PSU P4 that I can use? Any ideas? What would be my best options in this situation? Thanks!  
Dell PE T420 Non-redundant to Redundant Power Supply conversion