Please post brand and model of your " simple 3.5 mm to usb converter". Any link to a user manual or a brochure? If that 3.5mm jack is meant for a microphone, it might already offer the possibility of powering an electret microphone . Or you can build a battery supply adapter (9V battery and even 2 x AA alkalines) inside a small box and insert it between microphone and adapter. Also post Microphone data.

If that 3.5mm jack is meant for a microphone, it might already offer the possibility of powering an electret microphone . Or you can build a battery supply adapter (9V battery and even 2 x AA alkalines) inside a small box and insert it between microphone and adapter.