nostr:npub1e7pd9g47g8vx0m2kgnfqsj8y8hwu6h53metl3j74x5p89jt3xc3q3hhktr USB-C power bricks have to have enough on-board smarts to negotiate what current/voltage to deliver: I'd guess dirty mains power repeatedly fuzzes or crashes the power brick's microcontroller so it keeps thrashing around and renegotiating what it's supposed to be delivering.