I thought that I had posted this already? The battery marked 400V is actually your DC power supply with filter caps. The graph shows the caps bleeding off when power is removed.

If you want to get fancy you can use a bar graph display. In that case you would not use the zener and the values of the divider would be selected to light all the LEDs of the graph when power is on. When power is off the LEDs would go out (one at a time) until the caps were completely bled off.

 

Here's a link to a LM3914 Bar Graph display. The rectangle (page 2) marked 0-5V signal source is where you would use a resistive voltage divider to bring your power supply voltage down to an acceptable level for the chip input.
http://www.national.com/ds/LM/LM3914.pdf