https://www.gm-volt.com/threads/2016-volt-120v-evse-is-l1-l2-conversion-capable.218442/
It's been tested that GM's OEM EVSE for the Gen 1 (circa 2013) and Gen 2 (circa 2016) Volt handles 240V. But it is hardwired to only offer 8A or 12A despite 240V typically having higher current capabilities.
The Spark EV used Gen 1 volt parts throughout its high voltage system. The EVSE will be no different. You're welcome to look at component ratings inside but you'll ruin its waterproof rating.
Technically the onboard charger is the hardwired module in the engine compartment, the thing in the trunk is an EVSE (electric vehicle service equipment).
You can get an OEM Volt or Spark EVSE on eBay easily enough. But don't bother with them and get yourself a modern one that has more functionality like what the users above have posted.
I would recommend Vevor EVSE's. Here's one that comes with nema 6-20 and 5-15 plugs:
https://m.vevor.com/portable-ev-cha...ging-station-for-sae-j1772-evs-p_010981245345