On an ISS Power supply.

“The ISS is currently home to…four 14,000-pound payload-holders called ExPRESS Logistics Carriers. Experiments from Earth like the laser-communicator OPALS fly up to Station and Lego-attach to these carriers, which provide them with a place to stay and, just as importantly, the electrical power and data links they need to do their jobs. But since 2013, scientists sending up payloads have had trouble with the on-orbit utility grid.”

“Right now, experiments need special power converters if they want to hook up with the carriers. And that’s because NASA made a mistake: Inside the carriers, some capacitors were installed incorrectly. …in the part of the carriers that powers payloads, engineers installed some capacitors backward.”

“In designing the carrier, engineers had first planned to use capacitors that they could hook in any which way. But then they had changed the design, swapping in one-way capacitors. In between, no one had updated the blueprints. And so the circuit makers had made the circuits exactly as instructed, not paying attention to which way the capacitors faced. All four on-orbit carriers and the in-space spare turned out to have the same problem.”

NASA’s Power Supply Mistake on the ISS Was Totally Avoidable