USB Killer "overview" waveform. The peak-to-peak AC voltage is 172 V, with a 138 V DC bias, giving a total peak voltage of 310 V. DC bias amplitude gradually decreases as stored energy goes down. The pulse stops after 20 seconds.
https://cybre.ams3.digitaloceanspaces.com/media_attachments/files/107/657/202/443/717/640/original/ddb045d92e66e35b.png