Elgato Stream Deck will get power from your Mac or PC, via the USB cable that is attached to it.
If you want to add a USB extension cable then only certain lengths of cable will work.
A 1 meter long USB extension cable (3.28 feet) or shorter is an ideal length, to make sure that Elgato Stream Deck gets enough power from the USB connection.
If you want to try a longer cable, then 2 or 3 meters may work, but we have not certified those lengths.
The main issue is that bus-powered USB devices can only work with certain cable lengths - if the cable gets too long, then not enough power or data is transferred.