Hi Gerry – I use my Heathkit IT-28 capacitor checker for reforming electrolytic caps.Its maximum voltage is 600 volts.
The eye tube provides a continuous leakage reading as I slowly step up the voltage and easy to see if the leakage starts to exceed an acceptable limit. Where does one find 1000 volt electrolytics. Highest rating I have found is 600 volts. If I needed a rating that high, I would likely use two 500’s in series.