The lamp was an LED lantern with built-in mains and solar chargers for its Ni-Cd battery pack, and a USB charger circuit that provided a 5 volt output for charging phones and the like. The problem [Mark] discovered was that the mains charger circuit did not have any mains isolation, being a simple capacitive voltage dropper feeding a rectifier. These circuits are very common because they are extremely cheap, and are perfectly safe when concealed within insulated mains-powered products with no external connections. In the case of [Mark]’s lantern though the USB charging socket provided that external connection, and thus access to a potential 120 VAC shock for anyone touching it while charging.
Plainly this lamp doesn’t conform to any of the required safety standards for mains-powered equipment, and we’re guessing that its design might have come about by an existing safe lamp being manufactured with an upgrade in the form of the USB charger. The write-up gives it a full examination, and includes a modification to safely charge it from a wall-wart or similar safe power supply. Definitely one to watch out for!
If you were wondering what the fault was with Mark’s lamp, it was those cheap NiCd batteries failing. He replaced them, but there are plenty of techniques to rejuvenate old NiCds, both backyard, and refined.