Megohmmeter, Insulation tester, megger
A tiny Stepup transformer can easily generate 1kV or even 5kV from an oscillator with centre tapped 9V. With a primary impedance  \$Zp, ~~Zout=Zp*n^2\$ so that for example with 1:200 turns ratio and &lt; 1 Ohm (switches + battery ESR+ primary winding DCR) becomes \$200^2=40k\$ which unregulated can give 200*9V= 1.8kV but regulated to  1kV or more rectified for DC testing is possible.

If primary was not current limited, Short cct. current(SCC) could be 50mA and  primary could be 200*50mA = 10A, so it is current limited on input , so that  output current (I expect)  is limited 1mA which is adequate for insulation test with BDV &lt; 1kV.  

add:  I see MEGGER products have both crank and 12V AA operation with 0.5 to 5kV selections ~ 1.5mA  +/-0.5

What does your tester specify or SCC?