I am using several Godox speedlights with my Nikon D500 for studio work. Is there a power supply that works with the flashes whether they are AA-powered or using a Godox VB18 li-ion battery?
Speedlights are designed to be small, light, portable and that requires battery power. There are no commercially available AC adapters for them so you can plug them into a wall outlet.
There is a li-ion rechargeable external battery pack you can use with the AA-powered "TT" speedlights, the Godox PB960 which can power two speedlights at once; and any number of conventional 8xAA-powered external battery packs for a single speedlight. But the "V" li-ion powered speedlights do not have an external battery pack port, and cannot be hooked up to it.
If you need Godox strobes in a studio setting to run off AC power while in use, then consider their manual AC-powered monolights (the Mk II, Mk III and MS series also have radio triggering built-in that allow for remote power and group control). Or the TTL/HSS AD li-ion battery-powered Witstro strobes that also have an optional AC-adapter (AD400 and AD600 models).