Most people see their refund go down, sometimes by a lot, after entering a second W-2 or other income. This is because we start you off with the full standard deduction, which we subtract from the income you’ve entered so far. This usually gives you an artificially low taxable income at first, which translates to an artificially high refund.
To read the entire TurboTax FAQ which has an example of how this works, see: Why did my refund drop when I entered a second W-2? and/or other income.