I have a Nokia Asha 501 Dual Sim phone which comes with the power supply as stated in the title. It recently broke, and I decided to test if the phone's USB port which I thought was only for data transfer will act as supply as well. It did, surprisingly for me. I have 3 chargers, one is an original firm charger from another device and others is cheap ones. The original one and one of cheap ones has 5V=2A and other cheap one is all from the question title (except 5V=450mA). I observed how they all charge the phone, and the cheap ones make the phone glitchy and heat the charger extremely fast. The original one seemingly charger fine, no extreme heat ups or glitches of the phone. However, are the supply specs itself safe? Will they fry the phone eventually and/or something?