I tested this with 2 different chargers of different current ratings. A standard 1 amp iPhone charger and a high quality 2.1 amp charger. Using software on my phone I was able to read the current being drawn. What I found was both chargers when hooked to this cable would only be able to deliver approximately 500ma. When going direct to the chargers the iPhone charger was giving me around 800ma and the 2.1 amp charger was giving me about 1200 ma. My phone was at about 78% charge so it wasn't going to draw max current. Yet either way when hooked to the extension cable, it was only able to pull down around 500ma. The phone is a Droid maxx for reference.