Problem in Relay

Hi, I'am now doing some evaluation for a certain SPDT relay. Can any one help why there are times that the Vdc that I use to energize the coil drops? To clear my question: My set up is that I use a DC supply which is 19V to charge a capacitor which will energize the coil once I disconnected the battery to the circuit. After some cycles of on and off my suppy suddenly drops to 16Vdc, which is not enough to energize the coil.

Please explain this. Thank you very much.