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Sapphire Radeon R9 270X
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At absolute best, I doubt you'd get more than 490 megahash per second with that card.
At current difficulty (59335351233.9), if you can get lucky enough to actually finish any shares before a block is solved, you *might* be able to earn 0.00013 BTC per month. At an exchange rate of $230/BTC, that works out to about $0.0299 per month.
Of course, there is no guarantee that the difficulty will stay the same for the next century. The difficulty is adjusted every 2 weeks so most likely you'll earn a lot less than that over time.
Meanwhile, the additional electricity that your computer will be using to run all that hashpower will probably cost you a lot more than that.
If the 500w PSU was actually pulling a full 500w continuously every second 24 hours a day for 30 days and doing nothing else other than bitcoin mining the whole time, then you would be using about 360 kilowatt hours per month. If your electricity costs (including all taxes and fees) works out to about $0.11 per kilowatt hour, then generating that $0.0299 per month will cost you about $39.60 per month.
As for a USB ASIC miner (or any other ASIC), there are a lot of variables that go into figuring out how much you can make with mining. You can control some of those variables, but some are completely out of your control. It will really depend on things like:
- How good of a miner you buy
- How much you spend on the miner
- How much your electricity costs per kilowatt hour (including all taxes and fees)
- How much additional cooling your equipment needs
- Which mining pool you choose to join
- How much maintenance your system needs
- How much the mining difficulty changes in the future
- What the bitcoin exchange rate is in the future
Edit: Updated my estimate of hashes per second for the graphics card based on feedback from odolvlobo.