PSX-AC may be a bit pricey, but if your running command locomotives, it's cheaper than a repair.
I just installed one on my track power channel and it detected a short where my ZW-L alone didn't. The short was due to a price sticker I missed on the bottom of the piece of Fastrack that was contacting center and outer rail tabs. The PSX tripped instantly. I'm not installing them on my accessory power channels.