Asus Transformer slow charge

My ASUS Transformer TF101 charges extremely slowly using the original power adapter. **I'm trying to figure out the cause.** Here are all my knowns: 1. The power block (wall to USB adapter) charges my mobile phone without issues 2. The power block plus ASUS cable turns on my Transformer if it is off, or wakes it up if it is sleeping (but charges extremely slowly) 3. The ASUS cable lets me MTP and all that from computer and tablet 4. I installed ICS when in April and now its running 4.0.3 5. The charger does charge, but extremely slowly both on Keyboard dock and Tablet (a few days to get to 20%) 6. It definitely has not been near water, dust, direct sunlight or particle accelerators From this I gauge: it's not the power block or the cable, and the only change was ICS a few months back which worked okay (first update was buggy, but the next one fixed this). *Anyone else had this or know why it could be?*