How to drain 500mA constantly from a single USB port
90% of computers and laptops do not rate limit the USB port. It's connected to the 5V rail.

Another 9% have some sort of limiting only when more than 500mA is pulled.

The last 1% adhere to the full USB spec. Only allows 100mA until enumerated.

These are for regular USB ports. There is the USB battery charging spec for high powered ports that is different. The proper way is that you need a USB peripheral, like a microcontroller, that enumerates as a USB device requesting 1 to 5 blocks/units of power.