Should I skip extension cords without a UL mark?

Yes — non-listed cords often lie about their ratings. A UL-listed cord has been tested to safely handle its claimed amps and volts, while a no-name cord might claim 15 amps but use 18-gauge wire that overheats. Without UL (or ETL, CSA), the manufacturer just printed numbers that look good. An underrated cord under load can melt and start fires, so pay extra for the UL mark or a trusted brand.