List of supported printers: https://github.com/pelya/android-print-plugin-cups/blob/master/supported-printers.txt
Printing through Android USB socket is not supported yet, only printing over network is supported.
Sources: https://github.com/pelya/android-print-plugin-cups
☆☆☆☆☆ This app gains new abilities as it's downloads increase:
★☆☆☆☆ 1 000 downloads: double-sided printing, multiple pages per sheet - ✔done!
★★☆☆☆ 5 000 downloads: set page margins, collate copies, booklet print.
★★★☆☆ 10 000 downloads: set paper type, printer tray, printer resolution.
★★★★☆ 50 000 downloads: print preview, zoom and reflow page content.
★★★★★ 100 000 downloads: support for USB printers.
☄☄☄☄☄ 500 000 downloads: support for old apps and Android versions, by adding another 'Share' option.