USB ports supply 5 volts. The 12v LED strip requires at least 9 volts. I bought a step-up DC-to-DC boost transformer circuit which can step up from 1.5v and up it up 24 or 32 volts. It took 5 volts from the USB port and boosted it up to 12 volts to the LED strip.
WARNING: Before connecting the output to any equipment, measure the output. The output voltage can vary widely depending on the input voltage. I fried an MP3 player module with 24 volts. So be careful. The circuit has a nut in the three-prong resistor which changes the output voltage. You can turn it several times in either direction to fine-tune the output voltage.
Plastic box housing the transformer circuit has 2.1 mm plug (12 v) and socket (5v). I also added a 2.1 mm socket to the LED strip and a plug to a USB cable. (The USB port on the cable from the power bank was custom-built. I use it for electronic testing.) The power bank is also a custom-built one from 18650 batteries salvaged from a laptop battery.