I want to display 10-8 in QComboBox item. But it displays "sup" tags.
the easiest way is to use special Unicode characters and use them in translation file (direct usage in code may be problematic):
10⁻⁸
If you don't like use translation file try this code:
ui->comboBox->addItem(QString::fromWCharArray(L"10\x207B\x2078"));
ui->comboBox->addItem(QString::fromWCharArray(L"10⁻⁸"));
On my Qt.5.2.1 (Linux) it works. Also pasting above string in designer also works.